Moving a Metadata LUN on StorNext 4.x

Robert Leong -

Moving a Metadata LUN on 4.x StorNext

Metadata movement is performed on a LUN level, meaning you must specify the source LUN and the destination LUN. The new sndiskmove command that accomplishes metadata movement has two arguments: a source and destination LUN.

The destination size must be equal to or larger to the source.

After movement is complete, the physical source disk can be removed.

Note:  Although a stripe group can consist of multiple disks or LUNs, the sndiskmove command moves only a single disk or LUN. Consequently, references to “stripe group” in this section refer to a single disk or LUN when migrating metadata with sndiskmove.

Caution:  The metadata/journal stripe group you want to move cannot contain data. Sndiskmove treats metadata and journal stripe groups the same way, so it doesn’t matter whether the stripe group you want to move is a metadata stripe group, a journal stripe group, or a combined metadata and journal stripe group. The only caveat is that stripe groups used for movement cannot contain data.  If you attempt to move a metadata/journal stripe group that contains data, data loss could occur.

Use the following procedure to move a metadata/journal stripe group from a source LUN to a destination LUN.

1.      Unmount (umount) and stop (cvadmin > stop ....) the file system on the MDS(s), do not do a cvfs stop or cvfs fullstop as some services are still required or other filesystems might still needs to be functional.

2.     If your StorNext configuration includes a failover environment, you must shut down any standby FSMs that would start when you shut down the primary FSM. The movement procedure will not complete successfully unless all FSMs are shut down.

Caution:  If you do not shut down standby FSMs, file system corruption or data loss could occur.

2.1   Comment out the filesystem in /usr/cvfs/config/fsmlist and /etc/fstab during the migration so the filesystem does not start if a reboot is required.

3.      (Optional) Run the cvfsck command on the file system. See Checking the File System.

3.1  The destination LUN will need a StorNext label (cvlabel), and the label type must match (VTOC or EFI).

4.     sndiskmove -b 64 <source-LUN-label-name> <destination-LUN-label-name>
(where:
-b 64 for using the maximum buffers
<source-LUN-label-name> is the source LUN from which the move starts, 
<destination-LUN-label-name> is the destination LUN to which you want to move data.)

During the move process StorNext appends “<source-LUN-label-name>.old” to the source-LUN-label-name. This is to avoid confusion because the destination LUN <destination-LUN-label-name> is renamed to <source-LUN-label-name> (the same name as the original label name.)

For example:

<source-LUN-label-name> becomes <source-LUN-label-name>.old

<destination-LUN-label-name> becomes <source-LUN-label-name> (the same name as the original stripe group)

Copy speed observed on DotHill RAID 1 to RAID 1 is 150 to 180MB/s.  300GB is about 40 minutes.

5.      Only if your system includes a standby FSM: After you run sndiskmove, rescan the disks on the standby FSM’s host by running cvadmin -e ‘disks refresh’. You must run cvadmin -e ‘disks refresh’ on all systems on which you have a configured FSM for the file system involved in the move.

5.1  Remove the comments in fsmlist and fstab

6.    Restart the FSM.

7.     Only if your system includes a standby FSM:  Restart the standby FSM.

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See also Migrating SpycerBox meta to SSD
http://support.dvsus.com/entries/22408062-Migrating-SpycerBox-meta-to-SSD

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