[LU-7771] ZFS MDT running with high fragmentation

• Type: Question/Request
• Resolution: Not a Bug
• Priority: Minor
• Affects Version/s: Lustre 2.8.0
• Labels: zfs
• Environment: CentOS 6.6, Lustre 2.7.64, ZFS 0.6.5.3
• Assignee: Andreas Dilger
• Reporter: Jeff Johnson (Inactive)

Description

After six months of production the LFS MDT (only one MDT, no DNE) is running a zpool fragmentation level of 86%.

The customer has concerns about the high fragmentation.

Q) Is there a long term risk, other than reduced performance, of running at a high fragmentation level?

Also, the only way I know to clear the fragmentation is to quiesce the LFS, go offline, zfs send the MDT pool to a remote pool. Destroy and recreate the MDT pool and zfs send the remote pool back to local.

Q) Is there another way of accomplishing this?

Running the mdt:zfs_send->remote_pool-destroy/recreate-remotepool:zfs_send_>new_mdt_pool process is akin to doing a block level dd backup of an ldiskfs MDT. I am all for the conservative path (with user data) but I want to inquire if there is a better path developed to reach the same result.

Thanks