Chapter 21. Managing RAID

Procedure

1. From the left pane of the Manual Partitioning window, select the required partition.
2. Under the Device(s) section, click Modify. The Configure Mount Point dialog box opens.
3. Select the disks that you want to include in the RAID device and click Select.
4. Click the Device Type drop-down menu and select RAID.
5. Click the File System drop-down menu and select your preferred file system type.
6. Click the RAID Level drop-down menu and select your preferred level of RAID.
7. Click Update Settings to save your changes.
8. Click Done to apply the settings to return to the Installation Summary window.

Procedure

1. Create a RAID of two block devices, for example /dev/sda1 and /dev/sdc1:

   # mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdc1
   mdadm: Defaulting to version 1.2 metadata
   mdadm: array /dev/md0 started.

   The level_value option defines the RAID level.

2. Optional: Check the status of the RAID:

   # mdadm --detail /dev/md0
   /dev/md0:
              Version : 1.2
        Creation Time : Thu Oct 13 15:17:39 2022
           Raid Level : raid0
           Array Size : 18649600 (17.79 GiB 19.10 GB)
         Raid Devices : 2
        Total Devices : 2
          Persistence : Superblock is persistent
   
          Update Time : Thu Oct 13 15:17:39 2022
                State : clean
       Active Devices : 2
      Working Devices : 2
       Failed Devices : 0
        Spare Devices : 0
   [...]

3. Optional: Observe the detailed information about each device in the RAID:

   # mdadm --examine /dev/sda1 /dev/sdc1
   /dev/sda1:
             Magic : a92b4efc
           Version : 1.2
       Feature Map : 0x1000
        Array UUID : 77ddfb0a:41529b0e:f2c5cde1:1d72ce2c
              Name : 0
     Creation Time : Thu Oct 13 15:17:39 2022
        Raid Level : raid0
      Raid Devices : 2
   [...]

4. Create a file system on the RAID drive:

   # mkfs -t xfs /dev/md0

   Replace xfs with the file system that you chose to format the drive with.

5. Create a mount point for RAID drive and mount it:

   # mkdir /mnt/raid1
   # mount /dev/md0 /mnt/raid1

   Replace /mnt/raid1 with the mount point.

   If you want that RHEL mounts the md0 RAID device automatically when the system boots, add an entry for your device to the /etc/fstab file:

   /dev/md0   /mnt/raid1 xfs  defaults   0 0

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 MDRAID device.

   

5. In the Create RAID Device dialog box, enter a name for the new RAID.
6. In the RAID Level drop-down list, select a level of RAID you want to use.

7. From the Chunk Size drop-down list, select the size from the list of available options.

   The Chunk Size value specifies how large each block is for data writing. For example, if the chunk size is 512 KiB, the system writes the first 512 KiB to the first disk, the second 512 KiB is written to the second disk, and the third chunk is written to the third disk. If you have three disks in your RAID, the fourth 512 KiB is written to the first disk again.

8. Select the disks you want to use for RAID.
9. Click Create.

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, ⋮, next to the RAID device you want to format.
4. From the drop-down menu, select Format.
5. In the Format dialog box, enter a name.
6. In the Mount Point field, add the mount path.
7. From the Type drop-down list, select the type of file system.

8. 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.

9. If you want to encrypt the volume, select the type of encryption from the Encryption drop-down menu.

   If you do not want to encrypt the volume, select No encryption.

10. In the At boot drop-down menu, select when you want to mount the volume.

11. In the Mount options section:

    1. Select the Mount read only checkbox if you want the to mount the volume as a read-only logical volume.
    2. Select the Custom mount options checkbox and add the mount options if you want to change the default mount option.

12. Format the RAID partition:

    • If you want to format and mount the partition, click the Format and mount button.

    • If you want to only format the partition, click the Format only button.

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

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 RAID device on which you want to create a partition table.
4. Click the menu button, ⋮ in the MDRAID device section.
5. From the drop-down menu, select Create partition table.

6. In the Initialize disk dialog box, select the following:

   1. Partitioning:

      • Compatible with all systems and devices (MBR)
      • Compatible with modern system and hard disks > 2TB (GPT)
      • No partitioning

   2. Overwrite:

      • 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 want 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.

7. Click Initialize.

   The partitioning table is created and you can now create partitions on that table.

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 RAID device on which you want to create a partition.
4. On the RAID device page, scroll to the GPT partitions section and click the menu button, ⋮, next to the partition table you created. It is named Free space by default.
5. Click Create partition.
6. In the Create partition dialog box, enter a name for the file system. Do not use spaces in the name.
7. In the Mount Point field, add the mount path.
8. In the Type drop-down list, select the type of file system.
9. In the Size field, set the size of the partition.

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 want 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. If you want to encrypt the volume, select the type of encryption in the Encryption drop-down menu.

    If you do not want to encrypt the volume, select No encryption.

12. In the At boot drop-down menu, select when you want to mount the volume.

13. In the Mount options section:

    1. Select the Mount read only checkbox if you want the to mount the volume as a read-only logical volume.
    2. Select the Custom mount options checkbox and add the mount options if you want to change the default mount option.

14. Create the partition:

    • If you want to create and mount the partition, click the Create and mount button.

    • If you want to only create the partition, click the Create only button.

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

      You can create more partitions after the partition is created.

      At this point, the system uses mounted and formatted RAID.

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 Create LVM2 volume group dialog box, enter a name for the new volume group.

6. From the Disks list, select a RAID device.

   If you do not see the RAID in the list, unmount the RAID from the system. The RAID device must not be in use by the RHEL 8 system.

7. Click Create.

Procedure

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

   ---
   - name: Configure the storage
     hosts: managed-node-01.example.com
     tasks:
       - name: Create a RAID on sdd, sde, sdf, and sdg
         ansible.builtin.include_role:
           name: rhel-system-roles.storage
         vars:
           storage_safe_mode: false
           storage_volumes:
             - name: data
               type: raid
               disks: [sdd, sde, sdf, sdg]
               raid_level: raid0
               raid_chunk_size: 32 KiB
               mount_point: /mnt/data
               state: present

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. Extend RAID partitions. For more information, see Resizing a partition with parted.

2. Extend RAID to the maximum of the partition capacity:

   # mdadm --grow --size=max /dev/md0

   To set a specific size, write the value of the --size parameter in kB, for example --size=524228.

3. Increase the size of file system. For example, if the volume uses XFS and is mounted to /mnt/, enter:

   # xfs_growfs /mnt/

Procedure

1. Shrink the file system. For more information, see Managing file systems.

2. Decrease the RAID to the size, for example to 512 MB:

   # mdadm --grow --size=524228 /dev/md0

   Write the --size parameter in kB.

3. Shrink the partition to the size you need.

Procedure

1. Convert the RAID /dev/md0 to RAID level 5:

   # mdadm --grow --level=5 -n 3 /dev/md0 --force

2. Add a new disk to the array:

   # mdadm --manage /dev/md0 --add /dev/sdd

Procedure

1. Copy the contents of the PowerPC Reference Platform (PReP) boot partition from /dev/sda1 to /dev/sdb1:

   # dd if=/dev/sda1 of=/dev/sdb1

2. Update the prep and boot flag on the first partition on both disks:

   $ parted /dev/sda set 1 prep on
   $ parted /dev/sda set 1 boot on
   
   $ parted /dev/sdb set 1 prep on
   $ parted /dev/sdb set 1 boot on

Procedure

1. Insert the install disk.
2. During the initial boot up, select Rescue Mode instead of Install or Upgrade. When the system fully boots into Rescue mode, you can see the command line terminal.

3. From this terminal, execute the following commands:

   1. Create RAID partitions on the target hard drives by using the parted command.
   2. Manually create raid arrays by using the mdadm command from those partitions using any and all settings and options available.
4. Optional: After creating arrays, create file systems on the arrays as well.
5. Reboot the computer and select Install or Upgrade to install. As the Anaconda installer searches the disks in the system, it finds the pre-existing RAID devices.
6. When asked about how to use the disks in the system, select Custom Layout and click Next. In the device listing, the pre-existing MD RAID devices are listed.
7. Select a RAID device and click Edit.
8. Configure its mount point and optionally the type of file system it should use if you did not create one earlier, and then click Done. Anaconda installs to this pre-existing RAID device, preserving the custom options you selected when you created it in Rescue Mode.

Procedure

1. Create the /etc/mdadm.conf configuration file for monitoring array by scanning the RAID details:

   # mdadm --detail --scan >> /etc/mdadm.conf

   Note, that ARRAY and MAILADDR are mandatory variables.

2. Open the /etc/mdadm.conf configuration file with a text editor of your choice and add the MAILADDR variable with the mail address for the notification. For example, add new line:

   MAILADDR example@example.com

   Here, example@example.com is an email address to which you want to receive the alerts from the array monitoring.

3. Save changes in the /etc/mdadm.conf file and close it.

Procedure

1. Check the failed disk:

   1. View the kernel logs:

      # journalctl -k -f

   2. Search for a message similar to the following:

      md/raid:md0: Disk failure on sdd, disabling device.
      
      md/raid:md0: Operation continuing on 3 devices.

   3. Press Ctrl+C on your keyboard to exit the journalctl program.

2. Mark the failed disk as faulty:

   # mdadm --manage /dev/md0 --fail /dev/sdd

3. Optional: Check if the failed disk was marked correctly:

   # mdadm --detail /dev/md0

   At the end of the output is a list of disks in the /dev/md0 RAID where the disk /dev/sdd has the faulty status:

   Number   Major   Minor   RaidDevice State
      0       8       16        0      active sync   /dev/sdb
      1       8       32        1      active sync   /dev/sdc
      -       0        0        2      removed
      3       8       64        3      active sync   /dev/sde
   
      2       8       48        -      faulty   /dev/sdd

4. Remove the failed disk from the RAID:

   # mdadm --manage /dev/md0 --remove /dev/sdd

   Warning

   If your RAID cannot withstand another disk failure, do not remove any disk until the new disk has the active sync status. You can monitor the progress using the watch cat /proc/mdstat command.

5. Add the new disk to the RAID:

   # mdadm --manage /dev/md0 --add /dev/sdf

   The /dev/md0 RAID now includes the new disk /dev/sdf and the mdadm service will automatically starts copying data to it from other disks.

Procedure

1. Check the array for the failed disks behavior:

   # echo check > /sys/block/md0/md/sync_action

   This checks the array and the /sys/block/md0/md/sync_action file shows the sync action.

2. Open the /sys/block/md0/md/sync_action file with the text editor of your choice and see if there is any message about disk synchronization failures.
3. View the /sys/block/md0/md/mismatch_cnt file. If the mismatch_cnt parameter is not 0, it means that the RAID disks need repair.

4. Repair the disks in the array:

   # echo repair > /sys/block/md0/md/sync_action

   This repairs the disks in the array and writes the result into the /sys/block/md0/md/sync_action file.

5. View the synchronization progress:

   # cat /sys/block/md0/md/sync_action
   repair
   
   # cat /proc/mdstat
   Personalities : [raid0] [raid6] [raid5] [raid4] [raid1]
   md0 : active raid1 sdg[1] dm-3[0]
         511040 blocks super 1.2 [2/2] [UU]
   unused devices: <none>