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10.5. Migrating Volumes

Data can be redistributed across bricks while the trusted storage pool is online and available.Before replacing bricks on the new servers, ensure that the new servers are successfully added to the trusted storage pool.

Note

Before performing a replace-brick operation, review the known issues related to replace-brick operation in the Red Hat Gluster Storage 3.1 Release Notes.
This procedure applies only when at least one brick from the subvolume to be replaced is online. In case of a Distribute volume, the brick that must be replaced must be online. In case of a Distribute-replicate, at least one brick from the subvolume from the replica set that must be replaced must be online.
To replace the entire subvolume with new bricks on a Distribute-replicate volume, follow these steps:
  1. Add the new bricks to the volume. 
    # gluster volume add-brick VOLNAME [replica <COUNT>] NEW-BRICK
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    Example 10.1. Adding a Brick to a Distribute Volume

    # gluster volume add-brick test-volume server5:/exp5
Add Brick successful
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  2. Verify the volume information using the command: 
    # gluster volume info
 Volume Name: test-volume
    Type: Distribute
    Status: Started
    Number of Bricks: 5
    Bricks:
    Brick1: server1:/exp1
    Brick2: server2:/exp2
    Brick3: server3:/exp3
    Brick4: server4:/exp4
    Brick5: server5:/exp5
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    Note

    In case of a Distribute-replicate volume, you must specify the replica count in the add-brick command and provide the same number of bricks as the replica count to the add-brick command.
  3. Remove the bricks to be replaced from the subvolume.
    1. Start the remove-brick operation using the command: 
      # gluster volume remove-brick VOLNAME [replica <COUNT>] <BRICK> start
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      Example 10.2. Start a remove-brick operation on a distribute volume

      # gluster volume remove-brick test-volume server2:/exp2 start
Remove Brick start successful
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    2. View the status of the remove-brick operation using the command: 
      # gluster volume remove-brick VOLNAME [replica <COUNT>] BRICK status
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      Example 10.3. View the Status of remove-brick Operation

      # gluster volume remove-brick test-volume server2:/exp2 status
Node     Rebalanced-files size        scanned failures status
------------------------------------------------------------------
server2  16               16777216    52      0        in progress
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      Keep monitoring the remove-brick operation status by executing the above command. When the value of the status field is set to complete in the output of remove-brick status command, proceed further.
    3. Commit the remove-brick operation using the command: 
      # gluster volume remove-brick VOLNAME [replica <COUNT>] <BRICK> commit
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      Example 10.4. Commit the remove-brick Operation on a Distribute Volume

      # gluster volume remove-brick test-volume server2:/exp2 commit
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    4. Verify the volume information using the command: 
      # gluster volume info
Volume Name: test-volume
Type: Distribute
Status: Started
Number of Bricks: 4
Bricks:
Brick1: server1:/exp1
Brick3: server3:/exp3
Brick4: server4:/exp4
Brick5: server5:/exp5
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    5. Verify the content on the brick after committing the remove-brick operation on the volume. If there are any files leftover, copy it through FUSE or NFS mount.
      1. Verify if there are any pending files on the bricks of the subvolume.
        Along with files, all the application-specific extended attributes must be copied. glusterFS also uses extended attributes to store its internal data. The extended attributes used by glusterFS are of the form trusted.glusterfs.*, trusted.afr.*, and trusted.gfid. Any extended attributes other than ones listed above must also be copied.
        To copy the application-specific extended attributes and to achieve a an effect similar to the one that is described above, use the following shell script:
        Syntax: 
        # copy.sh <glusterfs-mount-point> <brick>
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        Example 10.5. Code Snippet Usage

        If the mount point is /mnt/glusterfs and brick path is /export/brick1, then the script must be run as: 
        # copy.sh /mnt/glusterfs /export/brick
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        #!/bin/bash

MOUNT=$1
BRICK=$2

for file in `find $BRICK ! -type d`; do
    rpath=`echo $file | sed -e "s#$BRICK\(.*\)#\1#g"`
    rdir=`dirname $rpath`

    cp -fv $file $MOUNT/$rdir;

    for xattr in `getfattr -e hex -m. -d $file 2>/dev/null | sed -e '/^#/d' | grep -v -E "trusted.glusterfs.*" | grep -v -E "trusted.afr.*" | grep -v "trusted.gfid"`;
    do
        key=`echo $xattr | cut -d"=" -f 1`
        value=`echo $xattr | cut -d"=" -f 2`

        setfattr $MOUNT/$rpath -n $key -v $value
    done
done
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      2. To identify a list of files that are in a split-brain state, execute the command: 
        # gluster volume heal test-volume info split-brain
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      3. If there are any files listed in the output of the above command, compare the files across the bricks in a replica set, delete the bad files from the brick and retain the correct copy of the file. Manual intervention by the System Administrator would be required to choose the correct copy of file.
A single brick can be replaced during a hardware failure situation, such as a disk failure or a server failure. The brick that must be replaced could either be online or offline. This procedure is applicable for volumes with replication. In case of a Replicate or Distribute-replicate volume types, after replacing the brick, self-heal is triggered to heal the data on the new brick.
Procedure to replace an old brick with a new brick on a Replicate or Distribute-replicate volume:
  1. Ensure that the new brick (sys5:/home/gfs/r2_5) that replaces the old brick (sys0:/home/gfs/r2_0) is empty. Ensure that all the bricks are online. The brick that must be replaced can be in an offline state.
  2. Execute the replace-brick command with the force option: 
    # gluster volume replace-brick r2 sys0:/home/gfs/r2_0 sys5:/home/gfs/r2_5 commit force 
volume replace-brick: success: replace-brick commit successful
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  3. Check if the new brick is online. 
    # gluster volume status
Status of volume: r2 
Gluster process                    Port    Online    Pid 
--------------------------------------------------------- 
Brick sys5:/home/gfs/r2_5            49156    Y    5731 

Brick sys1:/home/gfs/r2_1            49153    Y    5354 

Brick sys2:/home/gfs/r2_2            49154    Y    5365 

Brick sys3:/home/gfs/r2_3            49155    Y    5376
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  4. Ensure that after the self-heal completes, the extended attributes are set to zero on the other bricks in the replica. 
    # getfattr -d -m. -e hex /home/gfs/r2_1 
getfattr: Removing leading '/' from absolute path names 
# file: home/gfs/r2_1 
security.selinux=0x756e636f6e66696e65645f753a6f626a6563745f723a66696c655f743a733000 
trusted.afr.r2-client-0=0x000000000000000000000000
trusted.afr.r2-client-1=0x000000000000000000000000 
trusted.gfid=0x00000000000000000000000000000001 
trusted.glusterfs.dht=0x0000000100000000000000007ffffffe
trusted.glusterfs.volume-id=0xde822e25ebd049ea83bfaa3c4be2b440
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    Note that in this example, the extended attributes trusted.afr.r2-client-0 and trusted.afr.r2-client-1 are set to zero.

Important

In case of a Distribute volume type, replacing a brick using this procedure will result in data loss.
  1. Replace a brick with a commit force option: 
    # gluster volume replace-brick VOLNAME <BRICK> <NEW-BRICK> commit force
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    Example 10.6. Replace a brick on a Distribute Volume

    # gluster volume replace-brick r2 sys0:/home/gfs/r2_0 sys5:/home/gfs/r2_5 commit force 
volume replace-brick: success: replace-brick commit successful
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  2. Verify if the new brick is online. 
    # gluster volume status
Status of volume: r2 
Gluster process                    Port    Online    Pid 
--------------------------------------------------------- 
Brick sys5:/home/gfs/r2_5            49156    Y    5731 

Brick sys1:/home/gfs/r2_1            49153    Y    5354 

Brick sys2:/home/gfs/r2_2            49154    Y    5365 

Brick sys3:/home/gfs/r2_3            49155    Y    5376
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Note

All the replace-brick command options except the commit force option are deprecated.
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