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5.4. Formatting and Mounting Bricks

To create a Red Hat Gluster Storage volume, specify the bricks that comprise the volume. After creating the volume, the volume must be started before it can be mounted.

5.4.1. Creating Bricks Manually
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Important

  • Red Hat supports formatting a Logical Volume using the XFS file system on the bricks.

5.4.1.1. Creating a Thinly Provisioned Logical Volume
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  1. Create a physical volume(PV) by using the pvcreate command. 
    # pvcreate --dataalignment alignment_value device
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    For example: 
    # pvcreate --dataalignment 1280K /dev/sdb
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    Here, /dev/sdb is a storage device.
    Use the correct dataalignment option based on your device. For more information, see Section 20.2, “Brick Configuration”

    Note

    The device name and the alignment value will vary based on the device you are using.
  2. Create a Volume Group (VG) from the PV using the vgcreate command: 
    # vgcreate --physicalextentsize alignment_value volgroup device
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    For example: 
    # vgcreate --physicalextentsize 1280K rhs_vg /dev/sdb
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  3. Create a thin-pool using the following commands: 
    # lvcreate --thin volgroup/poolname --size pool_sz --chunksize chunk_sz --poolmetadatasize metadev_sz --zero n
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    For example: 
    # lvcreate --thin rhs_vg/rhs_pool --size 2T --chunksize 1280K --poolmetadatasize 16G --zero n
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    Ensure you read Chapter 20, Tuning for Performance to select appropriate values for chunksize and poolmetadatasize.
  4. Create a thinly provisioned volume that uses the previously created pool by running the lvcreate command with the --virtualsize and --thin options: 
    # lvcreate --virtualsize size --thin volgroup/poolname --name volname
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    For example: 
    # lvcreate --virtualsize 1G --thin rhs_vg/rhs_pool --name rhs_lv
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    It is recommended that only one LV should be created in a thin pool.
  5. Format bricks using the supported XFS configuration, mount the bricks, and verify the bricks are mounted correctly. To enhance the performance of Red Hat Gluster Storage, ensure you read Chapter 20, Tuning for Performance before formatting the bricks.

    Important

    Snapshots are not supported on bricks formatted with external log devices. Do not use -l logdev=device option with mkfs.xfs command for formatting the Red Hat Gluster Storage bricks. 
    # mkfs.xfs -f -i size=512 -n size=8192 -d su=128k,sw=10 device
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    DEVICE is the created thin LV. The inode size is set to 512 bytes to accommodate for the extended attributes used by Red Hat Gluster Storage.
  6. Run # mkdir /mountpoint to create a directory to link the brick to. 
    # mkdir /rhgs
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  7. Add an entry in /etc/fstab: 
    /dev/volgroup/volname /mountpoint  xfs rw,inode64,noatime,nouuid,x-systemd.device-timeout=10min  1 2
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    For example: 
    /dev/rhs_vg/rhs_lv /rhgs  xfs rw,inode64,noatime,nouuid,x-systemd.device-timeout=10min  1 2
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  8. Run mount /mountpoint to mount the brick.
  9. Run the df -h command to verify the brick is successfully mounted: 
    # df -h
/dev/rhs_vg/rhs_lv   16G  1.2G   15G   7% /rhgs
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  10. If SElinux is enabled, then the SELinux labels that has to be set manually for the bricks created using the following commands: 
    # semanage fcontext -a -t glusterd_brick_t /rhgs/brick1
# restorecon -Rv /rhgs/brick1
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5.4.2. Using Subdirectory as the Brick for Volume
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You can create an XFS file system, mount them and point them as bricks while creating a Red Hat Gluster Storage volume. If the mount point is unavailable, the data is directly written to the root file system in the unmounted directory.
For example, the /rhgs directory is the mounted file system and is used as the brick for volume creation. However, for some reason, if the mount point is unavailable, any write continues to happen in the /rhgs directory, but now this is under root file system.
To overcome this issue, you can perform the below procedure.
During Red Hat Gluster Storage setup, create an XFS file system and mount it. After mounting, create a subdirectory and use this subdirectory as the brick for volume creation. Here, the XFS file system is mounted as /bricks. After the file system is available, create a directory called /rhgs/brick1 and use it for volume creation. Ensure that no more than one brick is created from a single mount. This approach has the following advantages:
  • When the /rhgs file system is unavailable, there is no longer/rhgs/brick1 directory available in the system. Hence, there will be no data loss by writing to a different location.
  • This does not require any additional file system for nesting.
Perform the following to use subdirectories as bricks for creating a volume:
  1. Create the brick1 subdirectory in the mounted file system. 
    # mkdir /rhgs/brick1
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    Repeat the above steps on all nodes.
  2. Create the Red Hat Gluster Storage volume using the subdirectories as bricks. 
    # gluster volume create distdata01 ad-rhs-srv1:/rhgs/brick1
ad-rhs-srv2:/rhgs/brick2
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  3. Start the Red Hat Gluster Storage volume. 
    # gluster volume start distdata01
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  4. Verify the status of the volume. 
    # gluster  volume status distdata01
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Note

If multiple bricks are used from the same server, then ensure the bricks are mounted in the following format. For example: 
# df -h

/dev/rhs_vg/rhs_lv1   16G  1.2G   15G   7% /rhgs1
/dev/rhs_vg/rhs_lv2   16G  1.2G   15G   7% /rhgs2
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Create a distribute volume with 2 bricks from each server. For example: 
# gluster volume create test-volume server1:/rhgs1/brick1 server2:/rhgs1/brick1 server1:/rhgs2/brick2 server2:/rhgs2/brick2
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5.4.3.  Reusing a Brick from a Deleted Volume
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Bricks can be reused from deleted volumes, however some steps are required to make the brick reusable.
Brick with a File System Suitable for Reformatting (Optimal Method)
Run # mkfs.xfs -f -i size=512 device to reformat the brick to supported requirements, and make it available for immediate reuse in a new volume.

Note

All data will be erased when the brick is reformatted.
File System on a Parent of a Brick Directory
If the file system cannot be reformatted, remove the whole brick directory and create it again.

5.4.4. Cleaning An Unusable Brick
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If the file system associated with the brick cannot be reformatted, and the brick directory cannot be removed, perform the following steps:
  1. Delete all previously existing data in the brick, including the .glusterfs subdirectory.
  2. Run # setfattr -x trusted.glusterfs.volume-id brick and # setfattr -x trusted.gfid brick to remove the attributes from the root of the brick.
  3. Run # getfattr -d -m . brick to examine the attributes set on the volume. Take note of the attributes.
  4. Run # setfattr -x attribute brick to remove the attributes relating to the glusterFS file system.
    The trusted.glusterfs.dht attribute for a distributed volume is one such example of attributes that need to be removed.
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