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Managing GlusterFS Volumes

This section describes how to perform common GlusterFS management operations, including the following:

Configuring Transport Types for a Volume

A volume can support one or more transport types for communication between clients and brick processes. There are three types of supported transport, which are tcp, rdma, and tcp,rdma.

To change the supported transport types of a volume, follow the procedure:

  1. Unmount the volume on all the clients using the following command:

    umount mount-point

  2. Stop the volumes using the following command:

    gluster volume stop <VOLNAME>

  3. Change the transport type. For example, to enable both tcp and rdma execute the followimg command:

    gluster volume set test-volume config.transport tcp,rdma OR tcp OR rdma

  4. Mount the volume on all the clients. For example, to mount using rdma transport, use the following command:

    mount -t glusterfs -o transport=rdma server1:/test-volume /mnt/glusterfs

Expanding Volumes

You can expand volumes, as needed, while the cluster is online and available. For example, you might want to add a brick to a distributed volume, thereby increasing the distribution and adding to the capacity of the GlusterFS volume.

Similarly, you might want to add a group of bricks to a distributed replicated volume, increasing the capacity of the GlusterFS volume.

Note
When expanding distributed replicated and distributed dispersed volumes, you need to add a number of bricks that is a multiple of the replica or disperse count. For example, to expand a distributed replicated volume with a replica count of 2, you need to add bricks in multiples of 2 (such as 4, 6, 8, etc.).

To expand a volume

  1. If they are not already part of the TSP, probe the servers which contain the bricks you want to add to the volume using the following command:

    gluster peer probe <SERVERNAME>

    For example:

    # gluster peer probe server4
Probe successful

  2. Add the brick using the following command:

    gluster volume add-brick <VOLNAME> <NEW-BRICK>

    For example:

    # gluster volume add-brick test-volume server4:/exp4
Add Brick successful

  3. Check the volume information using the following command:

    gluster volume info <VOLNAME>

    The command displays information similar to the following:

    Volume Name: test-volume
Type: Distribute
Status: Started
Number of Bricks: 4
Bricks:
Brick1: server1:/exp1
Brick2: server2:/exp2
Brick3: server3:/exp3
Brick4: server4:/exp4

  4. Rebalance the volume to ensure that files are distributed to the new brick.

    You can use the rebalance command as described in Rebalancing Volumes

Shrinking Volumes

You can shrink volumes, as needed, while the cluster is online and available. For example, you might need to remove a brick that has become inaccessible in a distributed volume due to hardware or network failure.

Note
Data residing on the brick that you are removing will no longer be accessible at the Gluster mount point. Note however that only the configuration information is removed - you can continue to access the data directly from the brick, as necessary.

When shrinking distributed replicated and distributed dispersed volumes, you need to remove a number of bricks that is a multiple of the replica or stripe count. For example, to shrink a distributed replicate volume with a replica count of 2, you need to remove bricks in multiples of 2 (such as 4, 6, 8, etc.). In addition, the bricks you are trying to remove must be from the same sub-volume (the same replica or disperse set).

Running remove-brick with the start option will automatically trigger a rebalance operation to migrate data from the removed-bricks to the rest of the volume.

To shrink a volume

  1. Remove the brick using the following command:

    gluster volume remove-brick <VOLNAME> <BRICKNAME> start

    For example, to remove server2:/exp2:

    # gluster volume remove-brick test-volume server2:/exp2 start
volume remove-brick start: success

  2. View the status of the remove brick operation using the following command:

    gluster volume remove-brick <VOLNAME> <BRICKNAME> status

    For example, to view the status of remove brick operation on server2:/exp2 brick:

    # gluster volume remove-brick test-volume server2:/exp2 status
                                Node  Rebalanced-files  size  scanned       status
                           ---------  ----------------  ----  -------  -----------
617c923e-6450-4065-8e33-865e28d9428f               34   340      162   in progress

  3. Once the status displays "completed", commit the remove-brick operation

    gluster volume remove-brick <VOLNAME> <BRICKNAME> commit

    In this example:

    # gluster volume remove-brick test-volume server2:/exp2 commit
Removing brick(s) can result in data loss. Do you want to Continue? (y/n) y
volume remove-brick commit: success
Check the removed bricks to ensure all files are migrated.
If files with data are found on the brick path, copy them via a gluster mount point before re-purposing the removed brick.

  4. Check the volume information using the following command:

    gluster volume info

    The command displays information similar to the following:

    # gluster volume info
Volume Name: test-volume
Type: Distribute
Status: Started
Number of Bricks: 3
Bricks:
Brick1: server1:/exp1
Brick3: server3:/exp3
Brick4: server4:/exp4

Replace faulty brick

Replacing a brick in a pure distribute volume

To replace a brick on a distribute only volume, add the new brick and then remove the brick you want to replace. This will trigger a rebalance operation which will move data from the removed brick.

NOTE: Replacing a brick using the 'replace-brick' command in gluster is supported only for pure replicate or distributed-replicate volumes.

Steps to remove brick Server1:/home/gfs/r2_1 and add Server1:/home/gfs/r2_2:

  1. Here is the initial volume configuration:

    Volume Name: r2
Type: Distribute
Volume ID: 25b4e313-7b36-445d-b524-c3daebb91188
Status: Started
Number of Bricks: 2
Transport-type: tcp
Bricks:
Brick1: Server1:/home/gfs/r2_0
Brick2: Server1:/home/gfs/r2_1

  2. Here are the files that are present on the mount:

    # ls
1  10  2  3  4  5  6  7  8  9

  3. Add the new brick - Server1:/home/gfs/r2_2 now:

    # gluster volume add-brick r2 Server1:/home/gfs/r2_2
volume add-brick: success

  4. Start remove-brick using the following command:

    # gluster volume remove-brick r2 Server1:/home/gfs/r2_1 start
volume remove-brick start: success
ID: fba0a488-21a4-42b7-8a41-b27ebaa8e5f4

  5. Wait until remove-brick status indicates that it is complete.

    # gluster volume remove-brick r2 Server1:/home/gfs/r2_1 status
                                Node Rebalanced-files          size       scanned      failures       skipped               status   run time in secs
                           ---------      -----------   -----------   -----------   -----------   -----------         ------------     --------------
                           localhost                5       20Bytes            15             0             0            completed               0.00

  6. Now we can safely remove the old brick, so commit the changes:

    # gluster volume remove-brick r2 Server1:/home/gfs/r2_1 commit
Removing brick(s) can result in data loss. Do you want to Continue? (y/n) y
volume remove-brick commit: success

  7. Here is the new volume configuration.

    Volume Name: r2
Type: Distribute
Volume ID: 25b4e313-7b36-445d-b524-c3daebb91188
Status: Started
Number of Bricks: 2
Transport-type: tcp
Bricks:
Brick1: Server1:/home/gfs/r2_0
Brick2: Server1:/home/gfs/r2_2

  8. Check the contents of the mount:

    # ls
1  10  2  3  4  5  6  7  8  9

Replacing bricks in Replicate/Distributed Replicate volumes

This section of the document describes how brick: Server1:/home/gfs/r2_0 is replaced with brick: Server1:/home/gfs/r2_5 in volume r2 with replica count 2.

    Volume Name: r2
    Type: Distributed-Replicate
    Volume ID: 24a0437a-daa0-4044-8acf-7aa82efd76fd
    Status: Started
    Number of Bricks: 2 x 2 = 4
    Transport-type: tcp
    Bricks:
    Brick1: Server1:/home/gfs/r2_0
    Brick2: Server2:/home/gfs/r2_1
    Brick3: Server1:/home/gfs/r2_2
    Brick4: Server2:/home/gfs/r2_3

Steps:

  1. Make sure there is no data in the new brick Server1:/home/gfs/r2_5
  2. Check that all the bricks are running. It is okay if the brick that is going to be replaced is down.

  3. Replace the brick with 'commit force' option. Please note that other variants of replace-brick command are not supported.

    • Execute replace-brick command

      # gluster volume replace-brick r2 Server1:/home/gfs/r2_0 Server1:/home/gfs/r2_5 commit force volume replace-brick: success: replace-brick commit successful

    • Check that the new brick is now online

      # gluster volume status Status of volume: r2 Gluster process Port Online Pid

      Brick Server1:/home/gfs/r2_5 49156 Y 5731 <---- new brick is online Brick Server2:/home/gfs/r2_1 49153 Y 5354 Brick Server1:/home/gfs/r2_2 49154 Y 5365 Brick Server2:/home/gfs/r2_3 49155 Y 5376

    • Users can track the progress of self-heal using: gluster volume heal [volname] info, or by checking the size of the new brick.

    • # gluster volume heal <volname> info will show that no heal is required when the data is fully synced to the replaced brick.

      # gluster volume heal r2 info Brick Server1:/home/gfs/r2_5 Number of entries: 0

      Brick Server2:/home/gfs/r2_1 Number of entries: 0

      Brick Server1:/home/gfs/r2_2 Number of entries: 0

      Brick Server2:/home/gfs/r2_3 Number of entries: 0

Rebalancing Volumes

After expanding a volume using the add-brick command, you may need to rebalance the data among the servers. New directories created after expanding or shrinking of the volume will be evenly distributed automatically. For all the existing directories, the distribution can be fixed by rebalancing the layout and/or data.

This section describes how to rebalance GlusterFS volumes in your storage environment, using the following common scenarios:

  • Fix Layout - Fixes the layout to use the new volume topology so that files can be distributed to newly added nodes.

  • Fix Layout and Migrate Data - Rebalances volume by fixing the layout to use the new volume topology and migrating the existing data.

Rebalancing Volume to Fix Layout Changes

Fixing the layout is necessary because the layout structure is static for a given directory. Even after new bricks are added to the volume, newly created files in existing directories will still be distributed only among the original bricks. The command gluster volume rebalance <volname> fix-layout start will fix the layout information so that the files can be created on the newly added bricks. When this command is issued, all the file stat information which is already cached will get revalidated.

As of GlusterFS 3.6, the assignment of files to bricks will take into account the sizes of the bricks. For example, a 20TB brick will be assigned twice as many files as a 10TB brick. In versions before 3.6, the two bricks were treated as equal regardless of size, and would have been assigned an equal share of files.

A fix-layout rebalance will only fix the layout changes and does not migrate data. If you want to migrate the existing data, use gluster volume rebalance <volume> start command to rebalance data among the servers.

To rebalance a volume to fix layout

  • Start the rebalance operation on any Gluster server using the following command:

# gluster volume rebalance <VOLNAME> fix-layout start

For example:

  # gluster volume rebalance test-volume fix-layout start
  Starting rebalance on volume test-volume has been successful

Rebalancing Volume to Fix Layout and Migrate Data

After expanding a volume using the add-brick respectively, you need to rebalance the data among the servers. A remove-brick command will automatically trigger a rebalance.

To rebalance a volume to fix layout and migrate the existing data

  • Start the rebalance operation on any one of the server using the following command:

# gluster volume rebalance <VOLNAME> start

For example:

  # gluster volume rebalance test-volume start
  Starting rebalancing on volume test-volume has been successful
  • Start the migration operation forcefully on any one of the servers using the following command:

# gluster volume rebalance <VOLNAME> start force

For example:

  # gluster volume rebalance test-volume start force
  Starting rebalancing on volume test-volume has been successful

A rebalance operation will attempt to balance the diskusage across nodes, therefore it will skip files where the move will result in a less balanced volume. This leads to link files that are still left behind in the system and hence may cause performance issues. The behaviour can be overridden with the force argument.

Displaying the Status of Rebalance Operation

You can display the status information about rebalance volume operation, as needed.

  • Check the status of the rebalance operation, using the following command:

# gluster volume rebalance <VOLNAME> status

For example:

  # gluster volume rebalance test-volume status
                                  Node  Rebalanced-files  size  scanned       status
                             ---------  ----------------  ----  -------  -----------
  617c923e-6450-4065-8e33-865e28d9428f               416  1463      312  in progress

The time to complete the rebalance operation depends on the number of files on the volume along with the corresponding file sizes. Continue checking the rebalance status, verifying that the number of files rebalanced or total files scanned keeps increasing.

For example, running the status command again might display a result similar to the following:

  # gluster volume rebalance test-volume status
                                  Node  Rebalanced-files  size  scanned       status
                             ---------  ----------------  ----  -------  -----------
  617c923e-6450-4065-8e33-865e28d9428f               498  1783      378  in progress

The rebalance status displays the following when the rebalance is complete:

  # gluster volume rebalance test-volume status
                                  Node  Rebalanced-files  size  scanned       status
                             ---------  ----------------  ----  -------  -----------
  617c923e-6450-4065-8e33-865e28d9428f               502  1873      334   completed

Stopping an Ongoing Rebalance Operation

You can stop the rebalance operation, if needed.

  • Stop the rebalance operation using the following command:

# gluster volume rebalance <VOLNAME> stop

For example:

  # gluster volume rebalance test-volume stop
                                  Node  Rebalanced-files  size  scanned       status
                             ---------  ----------------  ----  -------  -----------
  617c923e-6450-4065-8e33-865e28d9428f               59   590      244       stopped
  Stopped rebalance process on volume test-volume

Stopping Volumes

  1. Stop the volume using the following command:

    # gluster volume stop <VOLNAME>

    For example, to stop test-volume:

    # gluster volume stop test-volume
Stopping volume will make its data inaccessible. Do you want to continue? (y/n)

  2. Enter y to confirm the operation. The output of the command displays the following:

    Stopping volume test-volume has been successful

Deleting Volumes

  1. Delete the volume using the following command:

    # gluster volume delete <VOLNAME>

    For example, to delete test-volume:

    # gluster volume delete test-volume
Deleting volume will erase all information about the volume. Do you want to continue? (y/n)

  2. Enter y to confirm the operation. The command displays the following:

    Deleting volume test-volume has been successful

Triggering Self-Heal on Replicate

In replicate module, previously you had to manually trigger a self-heal when a brick goes offline and comes back online, to bring all the replicas in sync. Now the pro-active self-heal daemon runs in the background, diagnoses issues and automatically initiates self-healing every 10 minutes on the files which requireshealing.

You can view the list of files that need healing, the list of files which are currently/previously healed, list of files which are in split-brain state, and you can manually trigger self-heal on the entire volume or only on the files which need healing.

  • Trigger self-heal only on the files which requires healing:

# gluster volume heal <VOLNAME>

For example, to trigger self-heal on files which requires healing of test-volume:

  # gluster volume heal test-volume
  Heal operation on volume test-volume has been successful
  • Trigger self-heal on all the files of a volume:

# gluster volume heal <VOLNAME> full

For example, to trigger self-heal on all the files of of test-volume:

  # gluster volume heal test-volume full
  Heal operation on volume test-volume has been successful
  • View the list of files that needs healing:

# gluster volume heal <VOLNAME> info

For example, to view the list of files on test-volume that needs healing:

  # gluster volume heal test-volume info
  Brick server1:/gfs/test-volume_0
  Number of entries: 0

  Brick server2:/gfs/test-volume_1
  Number of entries: 101
  /95.txt
  /32.txt
  /66.txt
  /35.txt
  /18.txt
  /26.txt
  /47.txt
  /55.txt
  /85.txt
  ...
  • View the list of files that are self-healed:

# gluster volume heal <VOLNAME> info healed

For example, to view the list of files on test-volume that are self-healed:

  # gluster volume heal test-volume info healed
  Brick Server1:/gfs/test-volume_0
  Number of entries: 0

  Brick Server2:/gfs/test-volume_1
  Number of entries: 69
  /99.txt
  /93.txt
  /76.txt
  /11.txt
  /27.txt
  /64.txt
  /80.txt
  /19.txt
  /41.txt
  /29.txt
  /37.txt
  /46.txt
  ...
  • View the list of files of a particular volume on which the self-heal failed:

# gluster volume heal <VOLNAME> info failed

For example, to view the list of files of test-volume that are not self-healed:

  # gluster volume heal test-volume info failed
  Brick Server1:/gfs/test-volume_0
  Number of entries: 0

  Brick Server2:/gfs/test-volume_3
  Number of entries: 72
  /90.txt
  /95.txt
  /77.txt
  /71.txt
  /87.txt
  /24.txt
  ...
  • View the list of files of a particular volume which are in split-brain state:

# gluster volume heal <VOLNAME> info split-brain

For example, to view the list of files of test-volume which are in split-brain state:

  # gluster volume heal test-volume info split-brain
  Brick Server1:/gfs/test-volume_2
  Number of entries: 12
  /83.txt
  /28.txt
  /69.txt
  ...

  Brick Server2:/gfs/test-volume_3
  Number of entries: 12
  /83.txt
  /28.txt
  /69.txt
  ...

Non Uniform File Allocation

NUFA translator or Non Uniform File Access translator is designed for giving higher preference to a local drive when used in a HPC type of environment. It can be applied to Distribute and Replica translators; in the latter case it ensures that one copy is local if space permits.

When a client on a server creates files, the files are allocated to a brick in the volume based on the file name. This allocation may not be ideal, as there is higher latency and unnecessary network traffic for read/write operations to a non-local brick or export directory. NUFA ensures that the files are created in the local export directory of the server, and as a result, reduces latency and conserves bandwidth for that server accessing that file. This can also be useful for applications running on mount points on the storage server.

If the local brick runs out of space or reaches the minimum disk free limit, instead of allocating files to the local brick, NUFA distributes files to other bricks in the same volume if there is space available on those bricks.

NUFA should be enabled before creating any data in the volume.

Use the following steps to enable NUFA:

  • decide which group is going to be used for managing settings of your volume. Assuming .
  • define cluster.nufa enable for this group:

# echo "cluster.nufa=enable" | tee -a /var/lib/glusterd/groups/<GROUPNAME>

  • add your volume to the group

# gluster volume set <VOLNAME> group <GROUPNAME>

  • verify whether the nufa setting was set properly

# gluster volume info

Important

NUFA is supported under the following conditions:

  • Volumes with only one brick per server.
  • For use with a FUSE client. NUFA is not supported with NFS or SMB.
  • A client that is mounting a NUFA-enabled volume must be present within the trusted storage pool.

The NUFA scheduler also exists, for use with the Unify translator; see below.

volume bricks
  type cluster/nufa
  option local-volume-name brick1
  subvolumes brick1 brick2 brick3 brick4 brick5 brick6 brick7
end-volume
NUFA additional options
  • lookup-unhashed

This is an advanced option where files are looked up in all subvolumes if they are missing on the subvolume matching the hash value of the filename. The default is on.

  • local-volume-name

The volume name to consider local and prefer file creations on. The default is to search for a volume matching the hostname of the system.

  • subvolumes

This option lists the subvolumes that are part of this 'cluster/nufa' volume. This translator requires more than one subvolume.

BitRot Detection

With BitRot detection in Gluster, it's possible to identify "insidious" type of disk errors where data is silently corrupted with no indication from the disk to the storage software layer than an error has occured. This also helps in catching "backend" tinkering of bricks (where data is directly manipulated on the bricks without going through FUSE, NFS or any other access protocol(s).

BitRot detection is disbled by default and needs to be enabled to make use of other sub-commands.

  1. To enable bitrot detection for a given volume :

# gluster volume bitrot <VOLNAME> enable

and similarly to disable bitrot use:

# gluster volume bitrot <VOLNAME> disable

Note
Enabling bitrot spawns the Signer & Scrubber daemon per node. Signer is responsible for signing (calculating checksum for each file) an object and scrubber verifies the calculated checksum against the objects data.

  1. Scrubber daemon has three (3) throttling modes that adjusts the rate at which objects are verified.

     # volume bitrot <VOLNAME> scrub-throttle lazy
 # volume bitrot <VOLNAME> scrub-throttle normal
 # volume bitrot <VOLNAME> scrub-throttle aggressive

  2. By default scrubber scrubs the filesystem biweekly. It's possible to tune it to scrub based on predefined frequency such as monthly, etc. This can be done as shown below:

     # volume bitrot <VOLNAME> scrub-frequency daily
 # volume bitrot <VOLNAME> scrub-frequency weekly
 # volume bitrot <VOLNAME> scrub-frequency biweekly
 # volume bitrot <VOLNAME> scrub-frequency monthly

NOTE: Daily scrubbing would not be available with GA release.

  1. Scrubber daemon can be paused and later resumed when required. This can be done as shown below:

# volume bitrot <VOLNAME> scrub pause

and to resume scrubbing:

# volume bitrot <VOLNAME> scrub resume

Note
Signing cannot be paused (and resumed) and would always be active as long as bitrot is enabled for that particular volume.

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