Here's what I've done to reproduce this:

- remove a disk containing one leg of an LVM raid1 mirror
- do enough IO that a lengthy recovery will be required
- insert the removed disk
- let recovery begin, but deactivate the LV before it completes
- activate the LV

This is the point where the recovery should start back up, but it 
doesn't. I haven't tried this in a few weeks, but am happy to try it 
again if it would help.

Nate




On 02/25/2014 05:13 PM, Brassow Jonathan wrote:

On Feb 24, 2014, at 11:30 PM, NeilBrown wrote:

quoted

On Sat, 1 Feb 2014 09:35:20 -0500 Nate Dailey [off-list ref] wrote:

quoted

If an LVM raid1 recovery is interrupted by deactivating the LV, when the
LV is reactivated it comes up with both members in sync--the recovery
never completes.

I've been trying to figure out how to fix this. Does this approach look
okay? I'm not sure what else to use to determine that a member disk is
out of sync. It looks like if disk_recovery_offset in the superblock
were updated during the recovery, that would also cause it to resume
after interruption--but MD skips the recovery target disk when writing
superblocks, so this doesn't work.

Comments?

I know it is confusing, but this should really have gone to dm-devel rather
than linux-raid, to make sure Jon Brassow see it (hi Jon!).

Setting recovery_offset to 0 certainly looks wrong, it should be set to
  sb->disk_recovery_offset
like the code just above your change.
Why does the code there not meet your need.

Jon: can you help?

Sure, thanks for forwarding.

Could you describe first how you are creating the problem?

When I create a RAID1 LV, deactivate it, and reactivate it; I don't see it skip the sync.  Also, if I replace a single drive and cycle the LV, I don't see it skip the sync.  What steps am I missing?

  brassow