[Lustre-discuss] Migrating MDT volume to a new location

[Frederik Ferner]

Bob Ball wrote:
> Is there a recommended way to migrate an MDT (MGS is separate) volume 
> from one location to another on the same server?  This uses iSCSI volumes.
> 
> Lustre 1.8.4

We have recently migrated our MDT to an new volume to change the inode 
size. We used tar and getfattr/setfattr for this closely following the 
MDT backup and restore procedure from the manual. We did take our file 
system down completely for over a week over Christmas to do this, though 
  it could have possibly been quicker if we had not taken time off as 
well. We also did very careful checking of everything before bringing up 
the new MDT. This was on a file system with at that time about 90M files.

Be sure to use a tar version that has an efficient way to detect files 
that are completely sparse. We found that the version on RHEL5 did not 
have this and taking backups took very long, I think there is a thread 
on the list about this which has a link to a fixed tar version for RHEL5 
which we used in the end. Also, we did not use any --posix or --xattr 
option for tar as we found that this is broken and creates bogus files. 
We used plain 'tar --sparse'.

If you don't have to change any mkfs options (like inode size in our 
case), I suspect any block based copy mechanism like dd or pvmove is the 
better option, possibly followed by a resize.

Good luck,
Frederik

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Frederik Ferner
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Diamond Light Source Ltd.		mob:   +44 7917 08 5110
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