[linux-lvm] Scrub errors after extending LVM RAID1 mirror [full email]

Steve Dodd steved424 at gmail.com
Sat Feb 2 16:09:44 UTC 2019

I think I've finally nailed down a test case, if anyone is bored and wants
to play:


I can't file upstream as RH bugzilla is down at the moment..


On Sat, 2 Feb 2019 at 13:34, Steve Dodd <steved424 at gmail.com> wrote:

> Weirdly, I thought I had failed to reproduce this bug, but my auto-scrub
> job ran this morning (first Sat of month), and I got:
> 03:15:15: Starting scrub of rvg/test ...
> 03:15:15: ... scrub started ...
> 03:18:36: FAILED:      7926656 mismatches
> So I really have no idea what's going on there. I will wade through my
> bash history and see if I can see what I did last week and what triggered
> this..
> S.
> On Wed, 23 Jan 2019 at 10:46, Steve Dodd <steved424 at gmail.com> wrote:
>> Sorry, user error sent the last email before I'd finished typing, trying
>> again..
>> Hi everyone,
>> I am experiencing a mystery scrub failure after extending a particular LV
>> which is a raid1 type mirror. I am using Ubuntu 18.04, LVM
>> 2.02.176-4.1ubuntu3, Ubuntu kernel 4.15.0-29-generic. I mentioned this on
>> IRC, thought an email might reach more people and allow me to provide more
>> detail.
>> As far as I can tell, the LV was *not* created with --nosync:
>> # lvs rvg/backups
>>>   LV      VG  Attr       LSize  Pool Origin Data%  Meta%  Move Log
>>> Cpy%Sync Convert
>>>   backups rvg rwi-aor--- 96.64G
>>> 100.00
>> The only odd thing I tend to do is specify extents for the extension
>> manually, being a bit OCD about on disk segment layouts. Having mined
>> .bash_history, it seems that last time I ran:
>> lvextend -l+2561 rvg/backups /dev/sdc3:20480-23041 /dev/sdb3:80097-82658
>> After that, a *lvchange --syncaction check rvg/backups* showed a huge
>> number for raid_mismatch_count (seemed roughly consistent with the newly
>> extended portion not being synced), but dumping the actual filesystem with
>> partclone from both legs of the mirror through md5sum showed no
>> inconsistencies; the contents are mostly borg repositories and for good
>> measure I verified the data in those using borg as well - no problems.
>> After a full resync all is well again. This is the second time this
>> happened to me on the same LV (I think - certainly the same VG.)
>> Any clues? Any known bugs fixed recently that might not have made it into
>> Ubuntu 1804? I am trying to reproduce with a test LV but can't. Only other
>> thing I can think might be relevant was that the volume was mounted (but
>> quiescent) at the time.
>> Thanks,
>> Steve
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