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

[Josip Rodin]

@Donk yes, of course.

% ps auxfw | grep '[d]'meventd
root      3325  0.1  0.0 574972 18956 ?        S<Lsl Jan30  25:34 /sbin/dmeventd

% dpkg -l dmeventd | grep ^.i
ii  dmeventd                             2:1.02.77-6ubuntu2                    amd64        Linux Kernel Device Mapper event daemon

% egrep '^[^#]*(snapshot_autoextend|monitoring)' /etc/lvm/lvm.conf
    snapshot_autoextend_threshold = 80
    snapshot_autoextend_percent = 20
    monitoring = 1

And syslog actually mentions:

Feb 12 06:18:04 hostname lvm[3325]: Monitoring snapshot vgname-lvname

Yet, it never notices the increases, for example:

Feb 12 06:18:07 hostname kernel: [1102775.345351] device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.
Feb 12 06:18:07 drop kernel: [1102775.345746] Buffer I/O error on device dm-0, logical block 60118
...

% sudo dmsetup info --noheadings -c -o name /dev/dm-0
vgname-lvname

Now you could say this particular one happened three seconds later and
it never had the chance, but it actually just never happens, over months
of usage.

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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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