Chapter 67. Configuring and managing logical volumes

Procedure

1. Identify the storage device you want to use as a physical volume. To list all available storage devices, use:

   $ lsblk

2. Create an LVM physical volume:

   # pvcreate /dev/sdb

   Replace /dev/sdb with the name of the device you want to initialize as a physical volume.

Procedure

1. List the physical volumes to identify the device you want to remove:

   # pvs
   
     PV           VG Fmt  Attr PSize  PFree
     /dev/sdb1       lvm2 ---  28.87g 28.87g

2. Remove the physical volume:

   # pvremove /dev/sdb1

   Replace /dev/sdb1 with the name of the device associated with the physical volume.

Procedure

1. Log in to the RHEL 8 web console.

   For details, see Logging in to the web console.

2. Click Storage.
3. In the Storage table, click the volume group in which you want to create logical volumes.
4. On the Logical volume group page, scroll to the LVM2 logical volumes section and click Create new logical volume.
5. In the Name field, enter a name for the new logical volume. Do not include spaces in the name.

6. In the Purpose drop-down menu, select Block device for filesystems.

   This configuration enables you to create a logical volume with the maximum volume size which is equal to the sum of the capacities of all drives included in the volume group.

   

7. Define the size of the logical volume. Consider:

   • How much space the system using this logical volume will need.
   • How many logical volumes you want to create.

   You do not have to use the whole space. If necessary, you can grow the logical volume later.

   

8. Click Create.

   The logical volume is created. To use the logical volume you must format and mount the volume.

Procedure

1. Log in to the RHEL 8 web console.

   For details, see Logging in to the web console.

2. Click Storage.
3. In the Storage table, click the volume group in the logical volumes is created.
4. On the Logical volume group page, scroll to the LVM2 logical volumes section.
5. Click the menu button, ⋮, next to the volume group you want to format.

6. From the drop-down menu, select Format.

   

7. In the Name field, enter a name for the file system.

8. In the Mount Point field, add the mount path.

   

9. In the Type drop-down menu, select a file system:

   • XFS file system supports large logical volumes, switching physical drives online without outage, and growing an existing file system. Leave this file system selected if you do not have a different strong preference.

     XFS does not support reducing the size of a volume formatted with an XFS file system

   • ext4 file system supports:

     • Logical volumes
     • Switching physical drives online without an outage
     • Growing a file system
     • Shrinking a file system

10. Select the Overwrite existing data with zeros checkbox if you want the RHEL web console to rewrite the whole disk with zeros. This option is slower because the program has to go through the whole disk, but it is more secure. Use this option if the disk includes any data and you need to overwrite it.

    If you do not select the Overwrite existing data with zeros checkbox, the RHEL web console rewrites only the disk header. This increases the speed of formatting.

11. From the Encryption drop-down menu, select the type of encryption if you want to enable it on the logical volume.

    You can select a version with either the LUKS1 (Linux Unified Key Setup) or LUKS2 encryption, which allows you to encrypt the volume with a passphrase.

12. In the At boot drop-down menu, select when you want the logical volume to mount after the system boots.
13. Select the required Mount options.

14. Format the logical volume:

    • If you want to format the volume and immediately mount it, click Format and mount.

    • If you want to format the volume without mounting it, click Format only.

      Formatting can take several minutes depending on the volume size and which formatting options are selected.

Verification

1. On the Logical volume group page, scroll to the LVM2 logical volumes section and click the logical volume to check the details and additional options.

   

2. If you selected the Format only option, click the menu button at the end of the line of the logical volume, and select Mount to use the logical volume.

Procedure

1. Log in to the RHEL web console.
2. Click Storage.
3. In the Storage table, click the volume group in the logical volumes is created.

4. On the Logical volume group page, scroll to the LVM2 logical volumes section and click the menu button, ⋮, next to volume group you want to resize.

   

5. From the menu, select Grow or Shrink to resize the volume:

   • Growing the Volume:

     1. Select Grow to increase the size of the volume.

     2. In the Grow logical volume dialog box, adjust the size of the logical volume.

        

     3. Click Grow.

        LVM grows the logical volume without causing a system outage.

   • Shrinking the Volume:

     1. Select Shrink to reduce the size of the volume.

     2. In the Shrink logical volume dialog box, adjust the size of the logical volume.

        

     3. Click Shrink.

        LVM shrinks the logical volume without causing a system outage.

Procedure

1. List and identify the PV that you want to include in the VG:

   # pvs

2. Create a VG:

   # vgcreate VolumeGroupName PhysicalVolumeName1 PhysicalVolumeName2

   Replace VolumeGroupName with the name of the volume group that you want to create. Replace PhysicalVolumeName with the name of the PV.

   To specify the extent size when creating a VG, use the -s ExtentSize option. Replace ExtentSize with the size of the extent. If you provide no size suffix, the command defaults to MB.

Procedure

1. Log in to the RHEL 8 web console.

   For details, see Logging in to the web console.

2. Click Storage.
3. In the Storage table, click the menu button.

4. From the drop-down menu, select Create LVM2 volume group.

   

5. In the Name field, enter a name for the volume group. The name must not include spaces.

6. Select the drives you want to combine to create the volume group.

   

   The RHEL web console displays only unused block devices. If you do not see your device in the list, make sure that it is not being used by your system, or format it to be empty and unused. Used devices include, for example:

   • Devices formatted with a file system
   • Physical volumes in another volume group
   • Physical volumes being a member of another software RAID device

7. Click Create.

   The volume group is created.

Procedure

1. List and identify the VG that you want to rename:

   # vgs

2. Rename the VG:

   # vgrename OldVolumeGroupName NewVolumeGroupName

   Replace OldVolumeGroupName with the name of the VG. Replace NewVolumeGroupName with the new name for the VG.

Procedure

1. List and identify the VG that you want to extend:

   # vgs

2. List and identify the PVs that you want to add to the VG:

   # pvs

3. Extend the VG:

   # vgextend VolumeGroupName PhysicalVolumeName

   Replace VolumeGroupName with the name of the VG. Replace PhysicalVolumeName with the name of the PV.

Procedure

1. List and identify the VG that you want to merge:

   # vgs
   
     VG               #PV #LV #SN Attr   VSize  VFree
     VolumeGroupName1   1   0   0 wz--n- 28.87g 28.87g
     VolumeGroupName2   1   0   0 wz--n-  1.88g  1.88g

2. Merge the source VG into the destination VG:

   # vgmerge VolumeGroupName2 VolumeGroupName1

   Replace VolumeGroupName2 with the name of the source VG. Replace VolumeGroupName1 with the name of the destination VG.

Procedure

1. If the physical volume is still being used, migrate the data to another physical volume from the same volume group:

   # pvmove /dev/vdb3
     /dev/vdb3: Moved: 2.0%
    ...
     /dev/vdb3: Moved: 79.2%
    ...
     /dev/vdb3: Moved: 100.0%

2. If there are not enough free extents on the other physical volumes in the existing volume group:

   1. Create a new physical volume from /dev/vdb4:

      # pvcreate /dev/vdb4
        Physical volume "/dev/vdb4" successfully created

   2. Add the newly created physical volume to the volume group:

      # vgextend VolumeGroupName /dev/vdb4
        Volume group "VolumeGroupName" successfully extended

   3. Move the data from /dev/vdb3 to /dev/vdb4:

      # pvmove /dev/vdb3 /dev/vdb4
        /dev/vdb3: Moved: 33.33%
        /dev/vdb3: Moved: 100.00%

3. Remove the physical volume /dev/vdb3 from the volume group:

   # vgreduce VolumeGroupName /dev/vdb3
   Removed "/dev/vdb3" from volume group "VolumeGroupName"

Procedure

1. Split the existing volume group VolumeGroupName1 to the new volume group VolumeGroupName2:

   # vgsplit VolumeGroupName1 VolumeGroupName2 /dev/vdb3
     Volume group "VolumeGroupName2" successfully split from "VolumeGroupName1"

   Note

   If you have created a logical volume using the existing volume group, use the following command to deactivate the logical volume:

   # lvchange -a n /dev/VolumeGroupName1/LogicalVolumeName

2. View the attributes of the two volume groups:

   # vgs
     VG                  #PV #LV #SN Attr   VSize  VFree
     VolumeGroupName1     2   1   0 wz--n- 34.30G 10.80G
     VolumeGroupName2     1   0   0 wz--n- 17.15G 17.15G

Procedure

1. Unmount the LogicalVolumeName logical volume:

   # umount /dev/mnt/LogicalVolumeName

2. Deactivate all logical volumes in the volume group, which prevents any further activity on the volume group:

   # vgchange -an VolumeGroupName
   vgchange -- volume group "VolumeGroupName" successfully deactivated

3. Export the volume group to prevent it from being accessed by the system from which you are removing it:

   # vgexport VolumeGroupName
   vgexport -- volume group "VolumeGroupName" successfully exported

4. View the exported volume group:

   # pvscan
     PV /dev/sda1    is in exported VG VolumeGroupName [17.15 GB / 7.15 GB free]
     PV /dev/sdc1    is in exported VG VolumeGroupName [17.15 GB / 15.15 GB free]
     PV /dev/sdd1    is in exported VG VolumeGroupName [17.15 GB / 15.15 GB free]
     ...

5. Shut down your system and unplug the disks that make up the volume group and connect them to the new system.

6. Plug the disks into the new system and import the volume group to make it accessible to the new system:

   # vgimport VolumeGroupName

   Note

   You can use the --force argument of the vgimport command to import volume groups that are missing physical volumes and subsequently run the vgreduce --removemissing command.

7. Activate the volume group:

   # vgchange -ay VolumeGroupName

8. Mount the file system to make it available for use:

   # mkdir -p /mnt/VolumeGroupName/users
   # mount /dev/VolumeGroupName/users /mnt/VolumeGroupName/users

Procedure

1. Ensure the volume group does not contain logical volumes:

   # vgs -o vg_name,lv_count VolumeGroupName
   
     VG               #LV
     VolumeGroupName    0

   Replace VolumeGroupName with the name of the volume group.

2. Remove the volume group:

   # vgremove VolumeGroupName

   Replace VolumeGroupName with the name of the volume group.

Procedure

1. Ensure the volume group does not contain logical volumes:

   # vgs -o vg_name,lv_count VolumeGroupName
   
     VG               #LV
     VolumeGroupName    0

   Replace VolumeGroupName with the name of the volume group.

2. Stop the lockspace on all nodes except the node where you are removing the volume group:

   # vgchange --lockstop VolumeGroupName

   Replace VolumeGroupName with the name of the volume group and wait for the lock to stop.

3. Remove the volume group:

   # vgremove VolumeGroupName

   Replace VolumeGroupName with the name of the volume group.

Prerequisites

1. You have created three or more physical volumes. For more information about creating physical volumes, see Creating LVM physical volume.
2. You have created the volume group. For more information, see Creating LVM volume group.

Procedure

1. Create a RAID0 logical volume from the existing volume group. The following command creates the RAID0 volume mylv from the volume group myvg, which is 2G in size, with three stripes and a stripe size of 4kB:

   # lvcreate --type raid0 -L 2G --stripes 3 --stripesize 4 -n mylv my_vg
     Rounding size 2.00 GiB (512 extents) up to stripe boundary size 2.00 GiB(513 extents).
     Logical volume "mylv" created.

2. Create a file system on the RAID0 logical volume. The following command creates an ext4 file system on the logical volume:

   # mkfs.ext4 /dev/my_vg/mylv

3. Mount the logical volume and report the file system disk space usage:

   # mount /dev/my_vg/mylv /mnt
   
   # df
   Filesystem             1K-blocks     Used  Available  Use% Mounted on
   /dev/mapper/my_vg-mylv   2002684     6168  1875072    1%   /mnt

Procedure

1. View the used and free space of physical volumes when using the LV:

   # pvs -o+pv_used
     PV          VG    Fmt    Attr   PSize      PFree     Used
    /dev/vdb1 myvg  lvm2   a--    1020.00m    0         1020.00m
    /dev/vdb2 myvg  lvm2   a--    1020.00m    0         1020.00m
    /dev/vdb3 myvg  lvm2   a--    1020.00m   1008.00m   12.00m

2. Move the data to other physical volume:

   1. If there are enough free extents on the other physical volumes in the existing volume group, use the following command to move the data:

      # pvmove /dev/vdb3
        /dev/vdb3: Moved: 2.0%
       ...
        /dev/vdb3: Moved: 79.2%
       ...
        /dev/vdb3: Moved: 100.0%

   2. If there are no enough free extents on the other physical volumes in the existing volume group, use the following commands to add a new physical volume, extend the volume group using the newly created physical volume, and move the data to this physical volume:

      # pvcreate /dev/vdb4
        Physical volume "/dev/vdb4" successfully created
      
      # vgextend myvg /dev/vdb4
        Volume group "myvg" successfully extended
      
      # pvmove /dev/vdb3 /dev/vdb4
        /dev/vdb3: Moved: 33.33%
        /dev/vdb3: Moved: 100.00%

3. Remove the physical volume:

   # vgreduce myvg /dev/vdb3
   Removed "/dev/vdb3" from volume group "myvg"

   If a logical volume contains a physical volume that fails, you cannot use that logical volume. To remove missing physical volumes from a volume group, you can use the --removemissing parameter of the vgreduce command, if there are no logical volumes that are allocated on the missing physical volumes:

   # vgreduce --removemissing myvg

Procedure

1. List the logical volumes and their paths:

   # lvs -o lv_name,lv_path
   
     LV                Path
     LogicalVolumeName /dev/VolumeGroupName/LogicalVolumeName

2. Check where the logical volume is mounted:

   # findmnt -o SOURCE,TARGET /dev/VolumeGroupName/LogicalVolumeName
   
   SOURCE                                        TARGET
   /dev/mapper/VolumeGroupName-LogicalVolumeName /MountPoint

   Replace /dev/VolumeGroupName/LogicalVolumeName with the path to your logical volume.

3. Unmount the logical volume:

   # umount /MountPoint

   Replace /MountPoint with the mounting point for your logical volume.

4. Remove the logical volume:

   # lvremove VolumeGroupName/LogicalVolumeName

   Replace VolumeGroupName/LogicalVolumeName with the path to your logical volume.

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   ---
   - name: Manage local storage
     hosts: managed-node-01.example.com
     tasks:
       - name: Resize LVM logical volume with file system
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.storage
         vars:
           storage_pools:
             - name: myvg
               disks:
                 - /dev/sda
                 - /dev/sdb
                 - /dev/sdc
               volumes:
                 - name: mylv1
                   size: 10 GiB
                   fs_type: ext4
                   mount_point: /opt/mount1
                 - name: mylv2
                   size: 50 GiB
                   fs_type: ext4
                   mount_point: /opt/mount2

   This playbook resizes the following existing file systems:

   • The Ext4 file system on the mylv1 volume, which is mounted at /opt/mount1, resizes to 10 GiB.
   • The Ext4 file system on the mylv2 volume, which is mounted at /opt/mount2, resizes to 50 GiB.

   For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.storage/README.md file on the control node.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Verification

1. Verify that the logical volume has been resized to the requested size:

   # ansible managed-node-01.example.com -m command -a 'lvs myvg'

2. Verify file system size using file system tools. For example, for ext4, calculate the file system size by multiplying block count and block size reported by dumpe2fs tool:

   # ansible managed-node-01.example.com -m command -a 'dumpe2fs -h /dev/myvg/mylv | grep -E "Block count|Block size"'

Prerequisites

1. You have enough free space on the underlying physical volumes (PVs) that make up the volume group (VG) to support the stripe.

Procedure

1. Optional: Display your volume group:

   # vgs
     VG      #PV #LV #SN Attr   VSize   VFree
     myvg     2   1   0 wz--n- 271.31G 271.31G

2. Optional: Create a stripe using the entire amount of space in the volume group:

   # lvcreate -n stripe1 -L 271.31G -i 2 myvg
     Using default stripesize 64.00 KB
     Rounding up size to full physical extent 271.31 GiB

3. Optional: Extend the myvg volume group by adding new physical volumes:

   # vgextend myvg /dev/sdc1
     Volume group "myvg" successfully extended

   Repeat this step to add sufficient physical volumes depending on your stripe type and the amount of space used. For example, for a two-way stripe that uses up the entire volume group, you need to add at least two physical volumes.

4. Extend the striped logical volume stripe1 that is a part of the myvg VG:

   # lvextend myvg/stripe1 -L 542G
     Using stripesize of last segment 64.00 KB
     Extending logical volume stripe1 to 542.00 GB
     Logical volume stripe1 successfully resized

   You can also extend the stripe1 logical volume to fill all of the unallocated space in the myvg volume group:

   # lvextend -l+100%FREE myvg/stripe1
     Size of logical volume myvg/stripe1 changed from 1020.00 MiB (255 extents) to <2.00 GiB (511 extents).
     Logical volume myvg/stripe1 successfully resized.

Procedure

1. Open the lvm.conf file in an editor of your choice.

2. Customize the lvm.conf file by uncommenting and modifying the setting for which you want to modify the default display values.

   • To customize what fields you see in the lvs output, uncomment the lvs_cols parameter and modify it:

       lvs_cols="lv_name,vg_name,lv_attr"

   • To hide empty fields for the pvs, vgs, and lvs commands, uncomment the compact_output=1 setting:

       compact_output = 1

   • To set gigabytes as the default unit for the pvs, vgs, and lvs commands, replace the units = "r" setting with units = "G":

       units = "G"

3. Ensure that the corresponding section of the lvm.conf file is uncommented. For example, to modify the lvs_cols parameter, the report section must be uncommented:

     report {
   ...
   }

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   ---
   - name: Manage local storage
     hosts: managed-node-01.example.com
     tasks:
       - name: Configure LVM pool with RAID
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.storage
         vars:
           storage_safe_mode: false
           storage_pools:
             - name: my_pool
               type: lvm
               disks: [sdh, sdi]
               raid_level: raid1
               volumes:
                 - name: my_volume
                   size: "1 GiB"
                   mount_point: "/mnt/app/shared"
                   fs_type: xfs
                   state: present

   For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.storage/README.md file on the control node.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Prerequisites

1. You have created three or more physical volumes. For more information about creating physical volumes, see Creating LVM physical volume.
2. You have created the volume group. For more information, see Creating LVM volume group.

Procedure

1. Create a RAID0 logical volume from the existing volume group. The following command creates the RAID0 volume mylv from the volume group myvg, which is 2G in size, with three stripes and a stripe size of 4kB:

   # lvcreate --type raid0 -L 2G --stripes 3 --stripesize 4 -n mylv my_vg
     Rounding size 2.00 GiB (512 extents) up to stripe boundary size 2.00 GiB(513 extents).
     Logical volume "mylv" created.

2. Create a file system on the RAID0 logical volume. The following command creates an ext4 file system on the logical volume:

   # mkfs.ext4 /dev/my_vg/mylv

3. Mount the logical volume and report the file system disk space usage:

   # mount /dev/my_vg/mylv /mnt
   
   # df
   Filesystem             1K-blocks     Used  Available  Use% Mounted on
   /dev/mapper/my_vg-mylv   2002684     6168  1875072    1%   /mnt

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   ---
   - name: Manage local storage
     hosts: managed-node-01.example.com
     tasks:
       - name: Configure stripe size for RAID LVM volumes
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.storage
         vars:
           storage_safe_mode: false
           storage_pools:
             - name: my_pool
               type: lvm
               disks: [sdh, sdi]
               volumes:
                 - name: my_volume
                   size: "1 GiB"
                   mount_point: "/mnt/app/shared"
                   fs_type: xfs
                   raid_level: raid0
                   raid_stripe_size: "256 KiB"
                   state: present

   For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.storage/README.md file on the control node.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Procedure

1. Create a RAID LV with DM integrity. The following example creates a new RAID LV with integrity named test-lv in the my_vg volume group, with a usable size of 256M and RAID level 1:

   # lvcreate --type raid1 --raidintegrity y -L 256M -n test-lv my_vg
   Creating integrity metadata LV test-lv_rimage_0_imeta with size 8.00 MiB.
   Logical volume "test-lv_rimage_0_imeta" created.
   Creating integrity metadata LV test-lv_rimage_1_imeta with size 8.00 MiB.
   Logical volume "test-lv_rimage_1_imeta" created.
   Logical volume "test-lv" created.

   Note

   To add DM integrity to an existing RAID LV, use the following command:

   # lvconvert --raidintegrity y my_vg/test-lv

   Adding integrity to a RAID LV limits the number of operations that you can perform on that RAID LV.

2. Optional: Remove the integrity before performing certain operations.

   # lvconvert --raidintegrity n my_vg/test-lv
   Logical volume my_vg/test-lv has removed integrity.

Procedure

1. Create a RAID logical volume:

   # lvcreate --type raid5 -i 3 -L 500M -n my_lv my_vg
   Using default stripesize 64.00 KiB.
   Rounding size 500.00 MiB (125 extents) up to stripe boundary size 504.00 MiB (126 extents).
   Logical volume "my_lv" created.

2. View the RAID logical volume:

   # lvs -a -o +devices,segtype
     LV               VG            Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                                                                 Type
     my_lv            my_vg         rwi-a-r--- 504.00m                                    100.00           my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0),my_lv_rimage_3(0) raid5
     [my_lv_rimage_0] my_vg         iwi-aor--- 168.00m                                                     /dev/sda(1)                                                             linear

3. Convert the RAID logical volume to another RAID level:

   # lvconvert --type raid6 my_vg/my_lv
   Using default stripesize 64.00 KiB.
   Replaced LV type raid6 (same as raid6_zr) with possible type raid6_ls_6.
   Repeat this command to convert to raid6 after an interim conversion has finished.
   Are you sure you want to convert raid5 LV my_vg/my_lv to raid6_ls_6 type? [y/n]: y
   Logical volume my_vg/my_lv successfully converted.

4. Optional: If this command prompts to repeat the conversion, run:

   # lvconvert --type raid6 my_vg/my_lv

Verification

1. View the RAID logical volume with the converted RAID level:

   # lvs -a -o +devices,segtype
     LV               VG            Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                                                                                   Type
     my_lv            my_vg         rwi-a-r--- 504.00m                                    100.00           my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0),my_lv_rimage_3(0),my_lv_rimage_4(0) raid6
     [my_lv_rimage_0] my_vg         iwi-aor--- 172.00m                                                     /dev/sda(1)                                                                               linear

Procedure

1. View the logical volume device that needs to be converted:

   # lvs -a -o name,copy_percent,devices my_vg
     LV     Copy%  Devices
     my_lv         /dev/sde1(0)

2. Convert the linear logical volume to a RAID device. The following command converts the linear logical volume my_lv in volume group __my_vg, to a 2-way RAID1 array:

   # lvconvert --type raid1 -m 1 my_vg/my_lv
     Are you sure you want to convert linear LV my_vg/my_lv to raid1 with 2 images enhancing resilience? [y/n]: y
     Logical volume my_vg/my_lv successfully converted.

Procedure

1. Display an existing LVM RAID1 logical volume:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
     [my_lv_rimage_0]        /dev/sde1(1)
     [my_lv_rimage_1]        /dev/sdf1(1)
     [my_lv_rmeta_0]         /dev/sde1(0)
     [my_lv_rmeta_1]         /dev/sdf1(0)

2. Convert an existing RAID1 LVM logical volume to an LVM linear logical volume. The following command converts the LVM RAID1 logical volume my_vg/my_lv to an LVM linear device:

   # lvconvert -m0 my_vg/my_lv
     Are you sure you want to convert raid1 LV my_vg/my_lv to type linear losing all resilience? [y/n]: y
     Logical volume my_vg/my_lv successfully converted.

   When you convert an LVM RAID1 logical volume to an LVM linear volume, you can also specify which physical volumes to remove. In the following example, the lvconvert command specifies that you want to remove /dev/sde1, leaving /dev/sdf1 as the physical volume that makes up the linear device:

   # lvconvert -m0 my_vg/my_lv /dev/sde1

Procedure

1. View the layout of a mirrored logical volume my_vg/my_lv:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv             15.20 my_lv_mimage_0(0),my_lv_mimage_1(0)
     [my_lv_mimage_0]        /dev/sde1(0)
     [my_lv_mimage_1]        /dev/sdf1(0)
     [my_lv_mlog]            /dev/sdd1(0)

2. Convert the mirrored logical volume my_vg/my_lv to a RAID1 logical volume:

   # lvconvert --type raid1 my_vg/my_lv
   Are you sure you want to convert mirror LV my_vg/my_lv to raid1 type? [y/n]: y
   Logical volume my_vg/my_lv successfully converted.

Procedure

1. Display the LVM device my_vg/my_lv, which is a 2-way RAID1 array:

   # lvs -a -o name,copy_percent,devices my_vg
     LV                Copy%  Devices
     my_lv             6.25    my_lv_rimage_0(0),my_lv_rimage_1(0)
     [my_lv_rimage_0]         /dev/sde1(0)
     [my_lv_rimage_1]         /dev/sdf1(1)
     [my_lv_rmeta_0]          /dev/sde1(256)
     [my_lv_rmeta_1]          /dev/sdf1(0)

   Metadata subvolumes named rmeta always exist on the same physical devices as their data subvolume counterparts rimage. The metadata/data subvolume pairs will not be created on the same physical volumes as those from another metadata/data subvolume pair in the RAID array unless you specify --alloc anywhere.

2. Convert the 2-way RAID1 logical volume my_vg/my_lv to a 3-way RAID1 logical volume:

   # lvconvert -m 2 my_vg/my_lv
   Are you sure you want to convert raid1 LV my_vg/my_lv to 3 images enhancing resilience? [y/n]: y
   Logical volume my_vg/my_lv successfully converted.

   The following are a few examples of changing the number of images in an existing RAID1 device:

   • You can also specify which physical volumes to use while adding an image to RAID. The following command converts the 2-way RAID1 logical volume my_vg/my_lv to a 3-way RAID1 logical volume by specifying the physical volume /dev/sdd1 to use for the array:

     # lvconvert -m 2 my_vg/my_lv /dev/sdd1

   • Convert the 3-way RAID1 logical volume into a 2-way RAID1 logical volume:

     # lvconvert -m1 my_vg/my_lv
     Are you sure you want to convert raid1 LV my_vg/my_lv to 2 images reducing resilience? [y/n]: y
     Logical volume my_vg/my_lv successfully converted.

   • Convert the 3-way RAID1 logical volume into a 2-way RAID1 logical volume by specifying the physical volume /dev/sde1, which contains the image to remove:

     # lvconvert -m1 my_vg/my_lv /dev/sde1

     Additionally, when you remove an image and its associated metadata subvolume volume, any higher-numbered images will be shifted down to fill the slot. Removing lv_rimage_1 from a 3-way RAID1 array that consists of lv_rimage_0, lv_rimage_1, and lv_rimage_2 results in a RAID1 array that consists of lv_rimage_0 and lv_rimage_1. The subvolume lv_rimage_2 will be renamed and take over the empty slot, becoming lv_rimage_1.

Procedure

1. Display the LVM device my_vg/my_lv, which is a 2-way RAID1 array:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv             12.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
     [my_lv_rimage_0]        /dev/sde1(1)
     [my_lv_rimage_1]        /dev/sdf1(1)
     [my_lv_rmeta_0]         /dev/sde1(0)
     [my_lv_rmeta_1]         /dev/sdf1(0)

2. Split the RAID image into a separate logical volume:

   • The following example splits a 2-way RAID1 logical volume, my_lv, into two linear logical volumes, my_lv and new:

     # lvconvert --splitmirror 1 -n new my_vg/my_lv
     Are you sure you want to split raid1 LV my_vg/my_lv losing all resilience? [y/n]: y

   • The following example splits a 3-way RAID1 logical volume, my_lv, into a 2-way RAID1 logical volume, my_lv, and a linear logical volume, new:

     # lvconvert --splitmirror 1 -n new my_vg/my_lv

Procedure

1. Create a RAID logical volume:

   # lvcreate --type raid1 -m 2 -L 1G -n my_lv my_vg
     Logical volume "my_lv" created

2. Optional: View the created RAID logical volume:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv          100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sdb1(1)
     [my_lv_rimage_1]        /dev/sdc1(1)
     [my_lv_rimage_2]        /dev/sdd1(1)
     [my_lv_rmeta_0]         /dev/sdb1(0)
     [my_lv_rmeta_1]         /dev/sdc1(0)
     [my_lv_rmeta_2]         /dev/sdd1(0)

3. Split an image from the created RAID logical volume and track the changes to the remaining array:

   # lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
     my_lv_rimage_2 split from my_lv for read-only purposes.
     Use 'lvconvert --merge my_vg/my_lv_rimage_2' to merge back into my_lv

4. Optional: View the logical volume after splitting the image:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
     [my_lv_rimage_0]        /dev/sdc1(1)
     [my_lv_rimage_1]          /dev/sdd1(1)
     [my_lv_rmeta_0]         /dev/sdc1(0)
     [my_lv_rmeta_1]         /dev/sdd1(0)

5. Merge the volume back into the array:

   # lvconvert --merge my_vg/my_lv_rimage_1
     my_vg/my_lv_rimage_1 successfully merged back into my_vg/my_lv

Procedure

1. View the RAID logical volume:

   # lvs -a -o name,copy_percent,devices my_vg
   
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sdb1(1)
     [my_lv_rimage_1]        /dev/sdc1(1)
     [my_lv_rimage_2]        /dev/sdd1(1)
     [my_lv_rmeta_0]         /dev/sdb1(0)
     [my_lv_rmeta_1]         /dev/sdc1(0)
     [my_lv_rmeta_2]         /dev/sdd1(0)

2. View the RAID logical volume if the /dev/sdb device fails:

   # lvs --all --options name,copy_percent,devices my_vg
   
     /dev/sdb: open failed: No such device or address
     Couldn't find device with uuid A4kRl2-vIzA-uyCb-cci7-bOod-H5tX-IzH4Ee.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rimage_1 while checking used and assumed devices.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rmeta_1 while checking used and assumed devices.
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        [unknown](1)
     [my_lv_rimage_1]        /dev/sdc1(1)
     [...]

   You can also view the system log for the error messages if the /dev/sdb device fails.

3. Set the raid_fault_policy field to allocate in the lvm.conf file:

    # vi /etc/lvm/lvm.conf
    raid_fault_policy = "allocate"

   Note

   If you set raid_fault_policy to allocate but there are no spare devices, the allocation fails, leaving the logical volume as it is. If the allocation fails, you can fix and replace the failed device by using the lvconvert --repair command. For more information, see Replacing a failed RAID device in a logical volume.

Procedure

1. View the RAID logical volume:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sdb1(1)
     [my_lv_rimage_1]        /dev/sdc1(1)
     [my_lv_rimage_2]        /dev/sdd1(1)
     [my_lv_rmeta_0]         /dev/sdb1(0)
     [my_lv_rmeta_1]         /dev/sdc1(0)
     [my_lv_rmeta_2]         /dev/sdd1(0)

2. Set the raid_fault_policy field to warn in the lvm.conf file:

   # vi /etc/lvm/lvm.conf
    # This configuration option has an automatic default value.
    raid_fault_policy = "warn"

3. View the system log to display error messages if the /dev/sdb device fails:

   # grep lvm /var/log/messages
   
   Apr 14 18:48:59 virt-506 kernel: sd 25:0:0:0: rejecting I/O to offline device
   Apr 14 18:48:59 virt-506 kernel: I/O error, dev sdb, sector 8200 op 0x1:(WRITE) flags 0x20800 phys_seg 0 prio class 2
   [...]
   Apr 14 18:48:59 virt-506 dmeventd[91060]: WARNING: VG my_vg is missing PV 9R2TVV-bwfn-Bdyj-Gucu-1p4F-qJ2Q-82kCAF (last written to /dev/sdb).
   Apr 14 18:48:59 virt-506 dmeventd[91060]: WARNING: Couldn't find device with uuid 9R2TVV-bwfn-Bdyj-Gucu-1p4F-qJ2Q-82kCAF.
   Apr 14 18:48:59 virt-506 dmeventd[91060]: Use 'lvconvert --repair my_vg/ly_lv' to replace failed device.

   If the /dev/sdb device fails, the system log displays error messages. In this case, however, LVM will not automatically attempt to repair the RAID device by replacing one of the images. Instead, if the device has failed you can replace the device with the --repair argument of the lvconvert command. For more information, see Replacing a failed RAID device in a logical volume.

Procedure

1. Create a RAID1 array:

   # lvcreate --type raid1 -m 2 -L 1G -n my_lv my_vg
     Logical volume "my_lv" created

2. Examine the created RAID1 array:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv            100.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sdb1(1)
     [my_lv_rimage_1]        /dev/sdb2(1)
     [my_lv_rimage_2]        /dev/sdc1(1)
     [my_lv_rmeta_0]         /dev/sdb1(0)
     [my_lv_rmeta_1]         /dev/sdb2(0)
     [my_lv_rmeta_2]         /dev/sdc1(0)

3. Replace the RAID device with any of the following methods depending on your requirements:

   1. Replace a RAID1 device by specifying the physical volume that you want to replace:

      # lvconvert --replace /dev/sdb2 my_vg/my_lv

   2. Replace a RAID1 device by specifying the physical volume to use for the replacement:

      # lvconvert --replace /dev/sdb1 my_vg/my_lv /dev/sdd1

   3. Replace multiple RAID devices at a time by specifying multiple replace arguments:

      # lvconvert --replace /dev/sdb1 --replace /dev/sdc1 my_vg/my_lv

Verification

1. Examine the RAID1 array after specifying the physical volume that you wanted to replace:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv             37.50 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sdb1(1)
     [my_lv_rimage_1]        /dev/sdc2(1)
     [my_lv_rimage_2]        /dev/sdc1(1)
     [my_lv_rmeta_0]         /dev/sdb1(0)
     [my_lv_rmeta_1]         /dev/sdc2(0)
     [my_lv_rmeta_2]         /dev/sdc1(0)

2. Examine the RAID1 array after specifying the physical volume to use for the replacement:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv             28.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
     [my_lv_rimage_0]        /dev/sda1(1)
     [my_lv_rimage_1]        /dev/sdd1(1)
     [my_lv_rmeta_0]         /dev/sda1(0)
     [my_lv_rmeta_1]         /dev/sdd1(0)

3. Examine the RAID1 array after replacing multiple RAID devices at a time:

   # lvs -a -o name,copy_percent,devices my_vg
     LV               Copy%  Devices
     my_lv             60.00 my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]        /dev/sda1(1)
     [my_lv_rimage_1]        /dev/sdd1(1)
     [my_lv_rimage_2]        /dev/sde1(1)
     [my_lv_rmeta_0]         /dev/sda1(0)
     [my_lv_rmeta_1]         /dev/sdd1(0)
     [my_lv_rmeta_2]         /dev/sde1(0)

Procedure

1. View the RAID logical volume:

   # lvs --all --options name,copy_percent,devices my_vg
     LV               Cpy%Sync Devices
     my_lv            100.00   my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]          /dev/sde1(1)
     [my_lv_rimage_1]          /dev/sdc1(1)
     [my_lv_rimage_2]          /dev/sdd1(1)
     [my_lv_rmeta_0]           /dev/sde1(0)
     [my_lv_rmeta_1]           /dev/sdc1(0)
     [my_lv_rmeta_2]           /dev/sdd1(0)

2. View the RAID logical volume after the /dev/sdc device fails:

   # lvs --all --options name,copy_percent,devices my_vg
     /dev/sdc: open failed: No such device or address
     Couldn't find device with uuid A4kRl2-vIzA-uyCb-cci7-bOod-H5tX-IzH4Ee.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rimage_1 while checking used and assumed devices.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rmeta_1 while checking used and assumed devices.
     LV               Cpy%Sync Devices
     my_lv            100.00   my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]          /dev/sde1(1)
     [my_lv_rimage_1]          [unknown](1)
     [my_lv_rimage_2]          /dev/sdd1(1)
     [my_lv_rmeta_0]           /dev/sde1(0)
     [my_lv_rmeta_1]           [unknown](0)
     [my_lv_rmeta_2]           /dev/sdd1(0)

3. Replace the failed device:

   # lvconvert --repair my_vg/my_lv
     /dev/sdc: open failed: No such device or address
     Couldn't find device with uuid A4kRl2-vIzA-uyCb-cci7-bOod-H5tX-IzH4Ee.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rimage_1 while checking used and assumed devices.
     WARNING: Couldn't find all devices for LV my_vg/my_lv_rmeta_1 while checking used and assumed devices.
   Attempt to replace failed RAID images (requires full device resync)? [y/n]: y
   Faulty devices in my_vg/my_lv successfully replaced.

4. Optional: Manually specify the physical volume that replaces the failed device:

   # lvconvert --repair my_vg/my_lv replacement_pv

5. Examine the logical volume with the replacement:

   # lvs --all --options name,copy_percent,devices my_vg
   
     /dev/sdc: open failed: No such device or address
     /dev/sdc1: open failed: No such device or address
     Couldn't find device with uuid A4kRl2-vIzA-uyCb-cci7-bOod-H5tX-IzH4Ee.
     LV               Cpy%Sync Devices
     my_lv            43.79    my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]          /dev/sde1(1)
     [my_lv_rimage_1]          /dev/sdb1(1)
     [my_lv_rimage_2]          /dev/sdd1(1)
     [my_lv_rmeta_0]           /dev/sde1(0)
     [my_lv_rmeta_1]           /dev/sdb1(0)
     [my_lv_rmeta_2]           /dev/sdd1(0)

   Until you remove the failed device from the volume group, LVM utilities still indicate that LVM cannot find the failed device.

6. Remove the failed device from the volume group:

   # vgreduce --removemissing my_vg

Verification

1. View the available physical volumes after removing the failed device:

   # pvscan
   PV /dev/sde1 VG rhel_virt-506 lvm2 [<7.00 GiB / 0 free]
   PV /dev/sdb1 VG my_vg lvm2 [<60.00 GiB / 59.50 GiB free]
   PV /dev/sdd1 VG my_vg lvm2 [<60.00 GiB / 59.50 GiB free]
   PV /dev/sdd1 VG my_vg lvm2 [<60.00 GiB / 59.50 GiB free]

2. Examine the logical volume after the replacing the failed device:

   # lvs --all --options name,copy_percent,devices my_vg
   my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
     [my_lv_rimage_0]          /dev/sde1(1)
     [my_lv_rimage_1]          /dev/sdb1(1)
     [my_lv_rimage_2]          /dev/sdd1(1)
     [my_lv_rmeta_0]           /dev/sde1(0)
     [my_lv_rmeta_1]           /dev/sdb1(0)
     [my_lv_rmeta_2]           /dev/sdd1(0)

Procedure

1. Optional: Control the rate at which a RAID logical volume is initialized by setting any one of the following options:

   • --maxrecoveryrate Rate[bBsSkKmMgG] sets the maximum recovery rate for a RAID logical volume so that it will not expel nominal I/O operations.

   • --minrecoveryrate Rate[bBsSkKmMgG] sets the minimum recovery rate for a RAID logical volume to ensure that I/O for sync operations achieves a minimum throughput, even when heavy nominal I/O is present

     # lvchange --maxrecoveryrate 4K my_vg/my_lv
     Logical volume _my_vg/my_lv_changed.

     Replace 4K with the recovery rate value, which is an amount per second for each device in the array. If you provide no suffix, the options assume kiB per second per device.

     # lvchange --syncaction repair my_vg/my_lv

     When you perform a RAID scrubbing operation, the background I/O required by the sync actions can crowd out other I/O to LVM devices, such as updates to volume group metadata. This might cause the other LVM operations to slow down.

     Note

     You can also use these maximum and minimum I/O rate while creating a RAID device. For example, lvcreate --type raid10 -i 2 -m 1 -L 10G --maxrecoveryrate 128 -n my_lv my_vg creates a 2-way RAID10 array my_lv, which is in the volume group my_vg with 3 stripes that is 10G in size with a maximum recovery rate of 128 kiB/sec/device.

2. Display the number of discrepancies in the array, without repairing them:

   # lvchange --syncaction check my_vg/my_lv

   This command initiates a background synchronization action on the array.

3. Optional: View the var/log/syslog file for the kernel messages.

4. Correct the discrepancies in the array:

   # lvchange --syncaction repair my_vg/my_lv

   This command repairs or replaces failed devices in a RAID logical volume. You can view the var/log/syslog file for the kernel messages after executing this command.

Verification

1. Display information about the scrubbing operation:

   # lvs -o +raid_sync_action,raid_mismatch_count my_vg/my_lv
   LV    VG    Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert SyncAction Mismatches
   my_lv my_vg rwi-a-r--- 500.00m                                    100.00           idle        0

Procedure

1. Create a RAID logical volume:

   # lvcreate --type raid5 -i 2 -L 500M -n my_lv my_vg
   
   Using default stripesize 64.00 KiB.
   Rounding size 500.00 MiB (125 extents) up to stripe boundary size 504.00 MiB (126 extents).
   Logical volume "my_lv" created.

2. View the RAID logical volume:

   # lvs -a -o +devices
   
   LV               VG    Attr       LSize   Pool   Origin Data% Meta% Move Log Cpy%Sync Convert Devices
   my_lv            my_vg rwi-a-r--- 504.00m                                    100.00            my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
   [my_lv_rimage_0] my_vg iwi-aor--- 252.00m                                                      /dev/sda(1)
   [my_lv_rimage_1] my_vg iwi-aor--- 252.00m                                                      /dev/sdb(1)
   [my_lv_rimage_2] my_vg iwi-aor--- 252.00m                                                      /dev/sdc(1)
   [my_lv_rmeta_0]  my_vg ewi-aor---   4.00m                                                      /dev/sda(0)
   [my_lv_rmeta_1]  my_vg ewi-aor---   4.00m                                                      /dev/sdb(0)
   [my_lv_rmeta_2]  my_vg ewi-aor---   4.00m                                                      /dev/sdc(0)

3. Optional: View the stripes images and stripesize of the RAID logical volume:

   # lvs -o stripes my_vg/my_lv
     #Str
        3

   # lvs -o stripesize my_vg/my_lv
     Stripe
     64.00k

4. Modify the attributes of the RAID logical volume by using the following ways depending on your requirement:

   1. Modify the stripes images of the RAID logical volume:

      # lvconvert --stripes 3 my_vg/my_lv
      Using default stripesize 64.00 KiB.
      WARNING: Adding stripes to active logical volume my_vg/my_lv will grow it from 126 to 189 extents!
      Run "lvresize -l126 my_vg/my_lv" to shrink it or use the additional capacity.
      Are you sure you want to add 1 images to raid5 LV my_vg/my_lv? [y/n]: y
      Logical volume my_vg/my_lv successfully converted.

   2. Modify the stripesize of the RAID logical volume:

      # lvconvert --stripesize 128k my_vg/my_lv
        Converting stripesize 64.00 KiB of raid5 LV my_vg/my_lv to 128.00 KiB.
      Are you sure you want to convert raid5 LV my_vg/my_lv? [y/n]: y
        Logical volume my_vg/my_lv successfully converted.

   3. Modify the maxrecoveryrate and minrecoveryrate attributes:

      # lvchange --maxrecoveryrate 4M my_vg/my_lv
        Logical volume my_vg/my_lv changed.

      # lvchange --minrecoveryrate 1M my_vg/my_lv
        Logical volume my_vg/my_lv changed.

   4. Modify the syncaction attribute:

      # lvchange --syncaction check my_vg/my_lv

   5. Modify the writemostly and writebehind attributes:

      # lvchange --writemostly /dev/sdb my_vg/my_lv
        Logical volume my_vg/my_lv changed.

      # lvchange --writebehind 100 my_vg/my_lv
        Logical volume my_vg/my_lv changed.

Verification

1. View the stripes images and stripesize of the RAID logical volume:

   # lvs -o stripes my_vg/my_lv
     #Str
        4

   # lvs -o stripesize my_vg/my_lv
     Stripe
     128.00k

2. View the RAID logical volume after modifying the maxrecoveryrate attribute:

   # lvs -a -o +raid_max_recovery_rate
     LV               VG       Attr        LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert MaxSync
     my_lv            my_vg    rwi-a-r---  10.00g                                     100.00           4096
     [my_lv_rimage_0] my_vg    iwi-aor---  10.00g
    [...]

3. View the RAID logical volume after modifying the minrecoveryrate attribute:

   # lvs -a -o +raid_min_recovery_rate
     LV               VG     Attr        LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert MinSync
     my_lv            my_vg  rwi-a-r---  10.00g                                     100.00           1024
     [my_lv_rimage_0] my_vg  iwi-aor---  10.00g
     [...]

4. View the RAID logical volume after modifying the syncaction attribute:

   # lvs -a
     LV               VG      Attr        LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
     my_lv            my_vg   rwi-a-r---  10.00g                                     2.66
     [my_lv_rimage_0] my_vg   iwi-aor---  10.00g
     [...]

Procedure

1. Create a RAID logical volume:

   # lvcreate --type raid1 -m 1 -L 10G test
     Logical volume "lvol0" created.

2. View the RAID logical volume:

   # lvs -a -o +devices,region_size
   
   LV                VG      Attr     LSize Pool Origin Data% Meta% Move Log   Cpy%Sync Convert Devices                              Region
   lvol0             test rwi-a-r--- 10.00g                                    100.00           lvol0_rimage_0(0),lvol0_rimage_1(0)  2.00m
   [lvol0_rimage_0]  test iwi-aor--- 10.00g                                                     /dev/sde1(1)                            0
   [lvol0_rimage_1]  test iwi-aor--- 10.00g                                                     /dev/sdf1(1)                            0
   [lvol0_rmeta_0]   test ewi-aor---  4.00m                                                     /dev/sde1(0)                            0
   [lvol0_rmeta_1]   test ewi-aor---  4.00m

   The Region column indicates the raid_region_size parameter’s value.

3. Optional: View the raid_region_size parameter’s value:

   # cat /etc/lvm/lvm.conf | grep raid_region_size
   
   # Configuration option activation/raid_region_size.
   	# raid_region_size = 2048

4. Change the region size of a RAID logical volume:

   # lvconvert -R 4096K my_vg/my_lv
   
   Do you really want to change the region_size 512.00 KiB of LV my_vg/my_lv to 4.00 MiB? [y/n]: y
     Changed region size on RAID LV my_vg/my_lv to 4.00 MiB.

5. Resynchronize the RAID logical volume:

   # lvchange --resync my_vg/my_lv
   
   Do you really want to deactivate logical volume my_vg/my_lv to resync it? [y/n]: y

Verification

1. View the RAID logical volume:

   # lvs -a -o +devices,region_size
   
   LV               VG   Attr        LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices                              Region
   lvol0            test rwi-a-r--- 10.00g                                    6.25           lvol0_rimage_0(0),lvol0_rimage_1(0)  4.00m
   [lvol0_rimage_0] test iwi-aor--- 10.00g                                                   /dev/sde1(1)                            0
   [lvol0_rimage_1] test iwi-aor--- 10.00g                                                   /dev/sdf1(1)                            0
   [lvol0_rmeta_0]  test ewi-aor---  4.00m                                                   /dev/sde1(0)                            0

   The Region column indicates the changed value of the raid_region_size parameter.

2. View the raid_region_size parameter’s value in the lvm.conf file:

   # cat /etc/lvm/lvm.conf | grep raid_region_size
   
   # Configuration option activation/raid_region_size.
   	# raid_region_size = 4096

Procedure

1. Create a logical volume named origin from the volume group vg001:

   # lvcreate -L 1G -n origin vg001

2. Create a snapshot named snap of /dev/vg001/origin LV that is 100 MB in size:

   # lvcreate --size 100M --name snap --snapshot /dev/vg001/origin

3. Display the origin volume and the current percentage of the snapshot volume being used:

   # lvs -a -o +devices
     LV      VG    Attr       LSize  Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
    origin vg001  owi-a-s---  1.00g                                                  /dev/sde1(0)
     snap vg001  swi-a-s--- 100.00m     origin 0.00                                 /dev/sde1(256)

Procedure

1. Merge the snapshot volume. The following command merges snapshot volume vg001/snap into its origin:

   # lvconvert --merge vg001/snap
   Merging of volume vg001/snap started.
     vg001/origin: Merged: 100.00%

2. View the origin volume:

   # lvs -a -o +devices
     LV      VG    Attr       LSize  Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
     origin vg001  owi-a-s---  1.00g                                                  /dev/sde1(0)

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   ---
   - name: Run the snapshot system role
     hosts: managed-node-01.example.com
     vars:
       snapshot_lvm_set:
         name: snapset1
         volumes:
           - name: data1 snapshot
             vg: data_vg
             lv: data1
             percent_space_required: 25
             mountpoint: /data1_snapshot
             options: nouuid
             mountpoint_create: true
           - name: data2 snapshot
             vg: data_vg
             lv: data2
             percent_space_required: 25
             mountpoint: /data2_snapshot
             options: nouuid
             mountpoint_create: true
     tasks:
       - name: Create a snapshot set
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.snapshot
         vars:
           snapshot_lvm_action: snapshot
       - name: Verify the set of snapshots for the LVs
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.snapshot
         vars:
           snapshot_lvm_action: check
           snapshot_lvm_verify_only: true
       - name: Mount the snapshot set
         ansible.builtin.include_role:
           name: redhat.rhel_system_roles.snapshot
         vars:
           snapshot_lvm_action: mount

   Here, the snapshot_lvm_set parameter describes specific logical volumes (LV) from the same volume group (VG). You can also specify LVs from different VGs while setting this parameter.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   • Unmount a specific LVM snapshot:

     ---
     - name: Unmount the snapshot specified by the snapset
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_snapset_name: snapset1
         snapshot_lvm_action: umount
         snapshot_lvm_vg: data_vg
         snapshot_lvm_lv: data2
         snapshot_lvm_mountpoint: /data2_snapshot
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_lv parameter describes a specific logical volume (LV) and the snapshot_lvm_vg parameter describes a specific volume group (VG).

   • Unmount a set of LVM snapshots:

     ---
     - name: Unmount a set of snapshots
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_action: umount
         snapshot_lvm_set:
           name: snapset1
           volumes:
             - name: data1 snapshot
               vg: data_vg
               lv: data1
               mountpoint: /data1_snapshot
             - name: data2 snapshot
               vg: data_vg
               lv: data2
               mountpoint: /data2_snapshot
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_set parameter describes specific LVs from the same VG. You can also specify LVs from different VGs while setting this parameter.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   • Extend all LVM snapshots by specifying the value for the percent_space_required parameter:

     ---
     - name: Extend all snapshots
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_action: extend
         snapshot_lvm_set:
           name: snapset1
           volumes:
             - name: data1 snapshot
               vg: data_vg
               lv: data1
               percent_space_required: 40
             - name: data2 snapshot
               vg: data_vg
               lv: data2
               percent_space_required: 40
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_set parameter describes specific LVs from the same VG. You can also specify LVs from different VGs while setting this parameter.

   • Extend a LVM snapshot set by setting percent_space_required to different value for each VG and LV pair in a set:

     ---
     - name: Extend the snapshot
       hosts: managed-node-01.example.com
       vars:
         snapshot_extend_set:
           name: snapset1
           volumes:
             - name: data1 snapshot
               vg: data_vg
               lv: data1
               percent_space_required: 30
             - name: data2 snapshot
               vg: data_vg
               lv: data2
               percent_space_required: 40
       tasks:
         - name: Extend data1 to 30% and data2 to 40%
           vars:
             snapshot_lvm_set: "{{ snapshot_extend_set }}"
             snapshot_lvm_action: extend
           ansible.builtin.include_role:
             name: redhat.rhel_system_roles.snapshot

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   • Revert a specific LVM snapshot to its original volume:

     ---
     - name: Revert a snapshot to its original volume
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_snapset_name: snapset1
         snapshot_lvm_action: revert
         snapshot_lvm_vg: data_vg
         snapshot_lvm_lv: data2
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_lv parameter describes a specific logical volume (LV) and the snapshot_lvm_vg parameter describes a specific volume group (VG).

   • Revert a set of LVM snapshots to its original volume:

     ---
     - name: Revert a set of snapshot
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_action: revert
         snapshot_lvm_set:
           name: snapset1
           volumes:
             - name: data1 snapshot
               vg: data_vg
               lv: data1
             - name: data2 snapshot
               vg: data_vg
               lv: data2
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_set parameter describes specific LVs from the same VG. You can also specify LVs from different VGs while setting this parameter.

     Note

     The revert operation might take some time to complete.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

4. Reboot the host, or deactivate and reactivate the logical volume using the following steps:

   $ umount /data1; umount /data2
   
   $ lvchange -an data_vg/data1 data_vg/data2
   
   $ lvchange -ay data_vg/data1 data_vg/data2
   
   $ mount /data1; mount /data2

Procedure

1. Create a playbook file, for example ~/playbook.yml, with the following content:

   • Remove a specific LVM snapshot:

     ---
     - name: Remove a snapshot
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_snapset_name: snapset1
         snapshot_lvm_action: remove
         snapshot_lvm_vg: data_vg
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_vg parameter describes a specific logical volume (LV) from the volume group (VG).

   • Remove a set of LVM snapshots:

     ---
     - name: Remove a set of snapshots
       hosts: managed-node-01.example.com
       vars:
         snapshot_lvm_action: remove
         snapshot_lvm_set:
           name: snapset1
           volumes:
             - name: data1 snapshot
               vg: data_vg
               lv: data1
             - name: data2 snapshot
               vg: data_vg
               lv: data2
       roles:
         - rhel-system-roles.snapshot

     Here, the snapshot_lvm_set parameter describes specific LVs from the same VG. You can also specify LVs from different VGs while setting this parameter.

2. Validate the playbook syntax:

   $ ansible-playbook --syntax-check ~/playbook.yml

   Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

3. Run the playbook:

   $ ansible-playbook ~/playbook.yml

Procedure

1. Create a thin pool:

   # lvcreate -L 100M -T vg001/mythinpool
     Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
     Logical volume "mythinpool" created.

   Note that since you are creating a pool of physical space, you must specify the size of the pool. The -T option of the lvcreate command does not take an argument; it determines what type of device is to be created from the other options that are added with the command. You can also create thin pool using additional parameters as shown in the following examples:

   • You can also create a thin pool using the --thinpool parameter of the lvcreate command. Unlike the -T option, the --thinpool parameter requires that you specify the name of the thin pool logical volume you are creating. The following example uses the --thinpool parameter to create a thin pool named mythinpool in the volume group vg001 that is 100M in size:

     # lvcreate -L 100M --thinpool mythinpool vg001
       Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
       Logical volume "mythinpool" created.

   • As striping is supported for pool creation, you can use the -i and -I options to create stripes. The following command creates a 100M thin pool named as thinpool in volume group vg001 with two 64 kB stripes and a chunk size of 256 kB. It also creates a 1T thin volume named vg001/thinvolume.

     Note

     Ensure that there are two physical volumes with sufficient free space in the volume group or you cannot create the thin pool.

     # lvcreate -i 2 -I 64 -c 256 -L 100M -T vg001/thinpool -V 1T --name thinvolume

2. Create a thin volume:

   # lvcreate -V 1G -T vg001/mythinpool -n thinvolume
     WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (100.00 MiB).
     WARNING: You have not turned on protection against thin pools running out of space.
     WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
     Logical volume "thinvolume" created.

   In this case, you are specifying virtual size for the volume that is greater than the pool that contains it. You can also create thin volumes using additional parameters as shown in the following examples:

   • To create both a thin volume and a thin pool, use the -T option of the lvcreate command and specify both the size and virtual size argument:

     # lvcreate -L 100M -T vg001/mythinpool -V 1G -n thinvolume
       Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
       WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (100.00 MiB).
       WARNING: You have not turned on protection against thin pools running out of space.
       WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
       Logical volume "thinvolume" created.

   • To use the remaining free space to create a thin volume and thin pool, use the 100%FREE option:

     # lvcreate -V 1G -l 100%FREE -T vg001/mythinpool -n thinvolume
     Thin pool volume with chunk size 64.00 KiB can address at most <15.88 TiB of data.
       Logical volume "thinvolume" created.

   • To convert an existing logical volume to a thin pool volume, use the --thinpool parameter of the lvconvert command. You must also use the --poolmetadata parameter in conjunction with the --thinpool parameter to convert an existing logical volume to a thin pool volume’s metadata volume.

     The following example converts the existing logical volume lv1 in volume group vg001 to a thin pool volume and converts the existing logical volume lv2 in volume group vg001 to the metadata volume for that thin pool volume:

     # lvconvert --thinpool vg001/lv1 --poolmetadata vg001/lv2
       Converted vg001/lv1 to thin pool.

     Note

     Converting a logical volume to a thin pool volume or a thin pool metadata volume destroys the content of the logical volume, as lvconvert does not preserve the content of the devices but instead overwrites the content.

   • By default, the lvcreate command approximately sets the size of the thin pool metadata logical volume by using the following formula:

     Pool_LV_size / Pool_LV_chunk_size * 64

     If you have large numbers of snapshots or if you have have small chunk sizes for your thin pool and therefore expect significant growth of the size of the thin pool at a later time, you may need to increase the default value of the thin pool’s metadata volume using the --poolmetadatasize parameter of the lvcreate command. The supported value for the thin pool’s metadata logical volume is in the range between 2MiB and 16GiB.

     The following example illustrates how to increase the default value of the thin pools’ metadata volume:

     # lvcreate -V 1G -l 100%FREE -T vg001/mythinpool --poolmetadatasize 16M -n thinvolume
     Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
        Logical volume "thinvolume" created.

3. View the created thin pool and thin volume:

   # lvs -a -o +devices
     LV                 VG    Attr       LSize   Pool       Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices
     [lvol0_pmspare]    vg001 ewi-------   4.00m                                                           /dev/sda(0)
     mythinpool         vg001 twi-aotz-- 100.00m                   0.00   10.94                            mythinpool_tdata(0)
     [mythinpool_tdata] vg001 Twi-ao---- 100.00m                                                           /dev/sda(1)
     [mythinpool_tmeta] vg001 ewi-ao----   4.00m                                                           /dev/sda(26)
     thinvolume         vg001 Vwi-a-tz--   1.00g mythinpool        0.00

4. Optional: Extend the size of a thin pool with the lvextend command. You cannot, however, reduce the size of a thin pool.

   Note

   This command fails if you use -l 100%FREE argument while creating a thin pool and thin volume.

   The following command resizes an existing thin pool that is 100M in size by extending it another 100M:

   # lvextend -L+100M vg001/mythinpool
     Size of logical volume vg001/mythinpool_tdata changed from 100.00 MiB (25 extents) to 200.00 MiB (50 extents).
     WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin pool vg001/mythinpool (200.00 MiB).
     WARNING: You have not turned on protection against thin pools running out of space.
     WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
   
     Logical volume vg001/mythinpool successfully resized

   # lvs -a -o +devices
     LV                 VG    Attr       LSize   Pool       Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices
     [lvol0_pmspare]    vg001 ewi-------   4.00m                                                           /dev/sda(0)
     mythinpool         vg001 twi-aotz-- 200.00m                   0.00   10.94                            mythinpool_tdata(0)
     [mythinpool_tdata] vg001 Twi-ao---- 200.00m                                                           /dev/sda(1)
     [mythinpool_tdata] vg001 Twi-ao---- 200.00m                                                           /dev/sda(27)
     [mythinpool_tmeta] vg001 ewi-ao----   4.00m                                                           /dev/sda(26)
     thinvolume         vg001 Vwi-a-tz--   1.00g mythinpool        0.00

5. Optional: To rename the thin pool and thin volume, use the following command:

   # lvrename vg001/mythinpool vg001/mythinpool1
     Renamed "mythinpool" to "mythinpool1" in volume group "vg001"
   
   # lvrename vg001/thinvolume vg001/thinvolume1
     Renamed "thinvolume" to "thinvolume1" in volume group "vg001"

   View the thin pool and thin volume after renaming:

   # lvs
     LV          VG       Attr     LSize   Pool       Origin Data%  Move Log Copy%  Convert
   mythinpool1 vg001   twi-a-tz 100.00m                     0.00
   thinvolume1 vg001   Vwi-a-tz   1.00g mythinpool1         0.00

6. Optional: To remove the thin pool, use the following command:

   # lvremove -f vg001/mythinpool1
     Logical volume "thinvolume1" successfully removed.
     Logical volume "mythinpool1" successfully removed.

Procedure

1. Log in to the RHEL 8 web console.

   For details, see Logging in to the web console.

2. Click Storage.
3. In the Storage table, click the volume group in which you want to create thin volumes.
4. On the Logical volume group page, scroll to the LVM2 logical volumes section and click Create new logical volume.
5. In the Name field, enter a name for the new logical volume. Do not include spaces in the name.

6. In the Purpose drop-down menu, select Pool for thinly provisioned volumes.

   This configuration enables you to create a logical volume with the maximum volume size which is equal to the sum of the capacities of all drives included in the volume group.

   

7. Define the size of the logical volume. Consider:

   • How much space the system using this logical volume needs.
   • How many logical volumes you want to create.

   You do not have to use the whole space. If necessary, you can grow the logical volume later.

   

8. Click Create.

   The pool for thin volumes is created and you can now add thin volumes to the pool.

Procedure

1. Log in to the RHEL 8 web console.

   For details, see Logging in to the web console.

2. Click Storage.
3. In the Storage table, click the menu button volume group in which you want to create thin volumes.
4. On the Logical volume group page, scroll to the LVM2 logical volumes section and click the pool in which you want to create the thin logical volumes.
5. On the Pool for thinly provisioned LVM2 logical volumes page, scroll to the Thinly provisioned LVM2 logical volumes section and click Create new thinly provisioned logical volume.
6. In the Create thin volume dialog box, enter a name for the thin volume. Do not use spaces in the name.
7. Define the size of the thin volume.

8. Click Create.

   The thin logical volume is created. You must format the volume before you can use it.

Procedure

1. Log in to the RHEL 8 web console.
2. Click Storage.
3. In the Storage table, click the volume group in which you want to create thin volumes.
4. On the Logical volume group page, scroll to the LVM2 logical volumes section and click the pool in which you want to create the thin logical volumes.
5. On the Pool for thinly provisioned LVM2 logical volumes page, scroll to the Thinly provisioned LVM2 logical volumes section and click the menu button, ⋮, next to the logical volume.

6. From the drop-down menu, select Create snapshot.

   

7. In the Name field, enter a snapshot name.

   

8. Click Create.
9. On the Pool for thinly provisioned LVM2 logical volumes page, scroll to the Thinly provisioned LVM2 logical volumes section and click the menu button, ⋮, next to the newly created snapshot.

10. From the drop-down menu, select Activate to activate the volume.

    

Procedure

1. Create a cachevol volume on the fast device:

   # lvcreate --size cachevol-size --name <fastvol> <vg> </dev/fast-pv>

   Replace the following values:

   cachevol-size

   The size of the cachevol volume, such as 5G

   fastvol

   A name for the cachevol volume

   vg

   The volume group name

   /dev/fast-pv

   The path to the fast block device, such as /dev/sdf

   Example 67.3. Creating a cachevol volume

   # lvcreate --size 5G --name fastvol vg /dev/sdf
   Logical volume "fastvol" created.

2. Attach the cachevol volume to the main logical volume to begin caching:

   # lvconvert --type cache --cachevol <fastvol> <vg/main-lv>

   Replace the following values:

   fastvol

   The name of the cachevol volume

   vg

   The volume group name

   main-lv

   The name of the slow logical volume

   Example 67.4. Attaching the cachevol volume to the main LV

   # lvconvert --type cache --cachevol fastvol vg/main-lv
   Erase all existing data on vg/fastvol? [y/n]: y
   Logical volume vg/main-lv is now cached.

Procedure

1. Create a cachepool volume on the fast device:

   # lvcreate --type cache-pool --size <cachepool-size> --name <fastpool> <vg /dev/fast>

   Replace the following values:

   cachepool-size

   The size of the cachepool, such as 5G

   fastpool

   A name for the cachepool volume

   vg

   The volume group name

   /dev/fast

   The path to the fast block device, such as /dev/sdf1

   Note

   You can use --poolmetadata option to specify the location of the pool metadata when creating the cache-pool.

   Example 67.5. Creating a cachepool volume

   # lvcreate --type cache-pool --size 5G --name fastpool vg /dev/sde
   Logical volume "fastpool" created.

2. Attach the cachepool to the main logical volume to begin caching:

   # lvconvert --type cache --cachepool <fastpool> <vg/main>

   Replace the following values:

   fastpool

   The name of the cachepool volume

   vg

   The volume group name

   main

   The name of the slow logical volume

   Example 67.6. Attaching the cachepool to the main LV

   # lvconvert --type cache --cachepool fastpool vg/main
   Do you want wipe existing metadata of cache pool vg/fastpool? [y/n]: y
   Logical volume vg/main is now cached.

Procedure

1. If the slow logical volume is active, deactivate it:

   # lvchange --activate n <vg>/<main-lv>

   Replace the following values:

   vg

   The volume group name

   main-lv

   The name of the slow logical volume

2. Create a deactivated cachevol volume on the fast device:

   # lvcreate --activate n --size <cachevol-size> --name <fastvol> <vg> </dev/fast-pv>

   Replace the following values:

   cachevol-size

   The size of the cachevol volume, such as 5G

   fastvol

   A name for the cachevol volume

   vg

   The volume group name

   /dev/fast-pv

   The path to the fast block device, such as /dev/sdf

   Example 67.7. Creating a deactivated cachevol volume

   # lvcreate --activate n --size 5G --name fastvol vg /dev/sdf
   WARNING: Logical volume vg/fastvol not zeroed.
   Logical volume "fastvol" created.

3. Attach the cachevol volume to the main logical volume to begin caching:

   # lvconvert --type writecache --cachevol <fastvol> <vg/main-lv>

   Replace the following values:

   fastvol

   The name of the cachevol volume

   vg

   The volume group name

   main-lv

   The name of the slow logical volume

   Example 67.8. Attaching the cachevol volume to the main LV

   # lvconvert --type writecache --cachevol fastvol vg/main-lv
   Erase all existing data on vg/fastvol? [y/n]?: y
   Using writecache block size 4096 for unknown file system block size, logical block size 512, physical block size 512.
   WARNING: unable to detect a file system block size on vg/main-lv
   WARNING: using a writecache block size larger than the file system block size may corrupt the file system.
   Use writecache block size 4096? [y/n]: y
   Logical volume vg/main-lv now has writecache.

4. Activate the resulting logical volume:

   # lvchange --activate y <vg/main-lv>

   Replace the following values:

   vg

   The volume group name

   main-lv

   The name of the slow logical volume

Procedure

1. Deactivate the logical volume:

   # lvchange --activate n <vg>/<main-lv>

   Replace vg with the volume group name, and main-lv with the name of the logical volume where caching is enabled.

2. Detach the cachevol or cachepool volume:

   # lvconvert --splitcache <vg>/<main-lv>

   Replace the following values:

   Replace vg with the volume group name, and main-lv with the name of the logical volume where caching is enabled.

   Example 67.9. Detaching the cachevol or cachepool volume

   # lvconvert --splitcache vg/main-lv
   Detaching writecache already clean.
   Logical volume vg/main-lv writecache has been detached.