[linux-lvm] LVM raid1 mirror: interrupted resync isn't handled well

[Nate Dailey]

Hi, looking for some guidance as to whether or not this is expected to
work, and if I'm doing anything wrong or can make any changes to fix this.

I've found that if LVM raid1 resync is interrupted, the volume
immediately comes up in sync when next activated, without actually
copying the remainder of the data.

I've reproduced this several times on a system with the root FS on an
LVM raid1 (note, this is not LVM on top of a separate MD raid1 device,
it's an LVM raid1 mirror created with 'lvconvert -m1 --type raid1 ...'):

- remove a disk containing one leg of an LVM raid1 mirror
- do enough IO that a lengthy resync will be required
- shutdown
- insert the removed disk
- reboot
- on reboot, the volume is resyncing properly
- before resync completes, reboot again
- this time during boot, the volume is activated and no resync is performed

But here's an example showing the same thing happening with just a
volume deactivate/activate:

# lvs
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert
...
testlv testvg rwi-a-r--- 5.00g 4.84

# lvchange -an /dev/testvg/testlv

# lvchange -ay /dev/testvg/testlv

# lvs
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert
...
testlv testvg rwi-a-r--- 5.00g 100.00

Here's dmesg showing the start of resync:

md/raid1:mdX: active with 1 out of 2 mirrors
created bitmap (5 pages) for device mdX
mdX: bitmap initialized from disk: read 1 pages, set 4524 of 10240 bits
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:dm-18
disk 1, wo:1, o:1, dev:dm-20
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:dm-18
disk 1, wo:1, o:1, dev:dm-20
md: recovery of RAID array mdX
md: minimum _guaranteed_ speed: 4000 KB/sec/disk.
md: using maximum available idle IO bandwidth (but not more than 15000
KB/sec) for recovery.
md: using 128k window, over a total of 5242880k.

And the interrupted sync:

md: md_do_sync() got signal ... exiting

And the reactivation without resuming resync:

md/raid1:mdX: active with 2 out of 2 mirrors
created bitmap (5 pages) for device mdX
mdX: bitmap initialized from disk: read 1 pages, set 3938 of 10240 bits


Can anyone offer any advice? Am I doing something wrong? Or is this just
a bug?

This is the lvm version (though I also grabbed the latest lvm2 from
git.fedorahosted.org and had the same problem):

LVM version: 2.02.100(2)-RHEL6 (2013-09-12)
Library version: 1.02.79-RHEL6 (2013-09-12)
Driver version: 4.23.6

I can try to dig through the sources to try to find the problem (I have
a fair amount of experience with MD debugging, none with LVM), but would
appreciate any advice as to where to start (is this likely to be a
problem in LVM, DM, MD, etc.).

Thanks!

Nate Dailey
Stratus Technologies