[Bug 1424114] Re: lvm snapshot is not being autoextended

[Josip Rodin]

I did some more testing with that trusty system and it does appear to be
working much better than before (i.e. not at all), though it seems there
are obfuscating circumstances - AFAICT it looks like it recognizes lost
causes (100.00% full snapshots) that it then no longer tries to extend,
but doesn't actually inform about them in a very meaningful way.

For example:

Feb 12 12:39:57 hostname lvm[3325]: Logical volume lvname successfully resized
Feb 12 12:39:59 hostname lvm[3325]: No longer monitoring snapshot vgname-lvname
Feb 12 12:40:00 hostname lvm[3325]: dm_task_run failed, errno = 22, Invalid argument

Here it did the extend but the next iteration didn't win the race and
just silently dropped the ball afterwards...?

Feb 12 12:44:39 hostname lvm[3325]: Snapshot vgname-lvname is now 92% full.
Feb 12 12:44:40 hostname lvm[3325]: device-mapper: waitevent ioctl on  failed: Interrupted system call
Feb 12 12:44:40 hostname lvm[3325]: device-mapper: waitevent ioctl on  failed: Interrupted system call
Feb 12 12:44:44 hostname lvm[3325]: Extending logical volume lvname to 252.00 MiB
Feb 12 12:44:44 hostname lvm[3325]: Monitoring snapshot vgname-lvname
Feb 12 12:44:44 hostname lvm[3325]: Logical volume lvname successfully resized
Feb 12 12:44:46 hostname lvm[3325]: No longer monitoring snapshot vgname-lvname

Here it looked like it was winning the race but inbetween it noticing it
should extend and actually extending, it actually lost the race, and
then the last message came with a larger lag...?

So it does appear that the original issue is fixed with the latest
trusty packages, with non-trivial caveats.

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https://bugs.launchpad.net/bugs/1424114

Title:
  lvm snapshot is not being autoextended

Status in lvm2 package in Ubuntu:
  Confirmed

Bug description:
  After setting auto extend threshold and rebooting, lvm snapshots are
  not being auto extended.

  Steps to recreate:
  1. Using Ubuntu 14.04 LTS
  2. Set snapshot_autoextend_threshold to less than 100
  # grep autoext /etc/lvm/lvm.conf 
      snapshot_autoextend_threshold = 50
      snapshot_autoextend_percent = 20
  3. Reboot server to have lvm reread lvm.conf
  4. Create a snapshot of a mounted logical volume
  # lvcreate -s /dev/testVG/testLV -L 1G -n testLVsnap
  5. Make modifications to mounted logical volume
  6. List logical volumes and snapshots
  # lvs
    LV         VG     Attr      LSize  Pool Origin Data%  Move Log Copy%  Convert
    testLV     testVG owi-aos-- 10.00g                                           
    testLVsnap testVG swi-a-s--  1.00g      testLV  95.04

  What I expected to have happened:
  Once Data% of snapshot reached the snapshot_autoextend_threshold, the snapshot logical volume should have been auto extended.

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