[Bug 1556602] Re: LVM in 16.04 cannot mount LVM Cached Volumes created in 15.10

[Ben McCann]

LVM caching enabled in Ubuntu 16.04 (or, to be completely honest, Linux
Mint 18) is also incompatible with the older caching implementation in
Linux Mint Debian Edition 2 (i.e. Debian Jessie). I hoped the following
procedure would create an LVM cache that works for both Jessie and
Xenial:

1) Under Jessie, remove the cache from the LVM volume.
2) Reboot into Xenial and add an LVM cache to the volume. (This works fine).
3) Reboot back to Jessie to use the LVM volume with caching created under Xenial.

My goal is to support dual boot between jessie and xenial with LVM
caching enabled on my data volumes.

This doesn't work. The LVM volume comes up a disabled or offline under
Jessie and there's no apparent way to bring it up without removing the
cache. (I can easily recreate this on my scratch/test machine in case
there's useful data to be gathered).

So, LVM caching between debian jessie and ubuntu xenial is neither
forward or backwards compatible.

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https://bugs.launchpad.net/bugs/1556602

Title:
  LVM in 16.04 cannot mount LVM Cached Volumes created in 15.10

Status in lvm2 package in Ubuntu:
  Confirmed

Bug description:
  I'm test driving Ubuntu Mate Beta 1 (from USB) on a machine that uses
  LVM caching. (I use some SSD to cache old hard drives). My LVM setup
  was created with Linux Mint Debian Edition - Betsy release.

  The system cannot mount these cached volumes due to the following
  error reported by 'pvs':

  ubuntu-mate at ubuntu-mate:~$ sudo pvs
    LV CacheArchive has invalid cache's feature flag.
    LV CacheArchive is missing cache policy name.
    Internal error: LV segments corrupted in CacheArchive.
    LV CacheArchive has invalid cache's feature flag.
    LV CacheArchive is missing cache policy name.
    Internal error: LV segments corrupted in CacheArchive.
    PV         VG   Fmt  Attr PSize   PFree 
    /dev/sda5  vga  lvm2 a--   80.00g 70.00g
    /dev/sda6  vga  lvm2 a--  160.00g 50.00g
    /dev/sdb1  vga  lvm2 a--  200.00g 50.00g

  I did a bit of googling and found a similar report for upgrades from
  Fedora 21 to Fedora 23. See
  https://bugzilla.redhat.com/show_bug.cgi?id=1282188.

  I'll annotate this bug with the LVM version from my existing Debian
  based configuration in a few minutes.

  This is a show-stopper for me because I use LVM caching on both of my
  PCs. It's a great way to marry a 256 GB SSD with a 2 TB hard drive. I
  keep the OS and some key partitions on the SSD and then use the rest
  of the SSD to cache the hard drive.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: lvm2 2.02.133-1ubuntu7
  ProcVersionSignature: Ubuntu 4.4.0-7.22-generic 4.4.2
  Uname: Linux 4.4.0-7-generic x86_64
  ApportVersion: 2.20-0ubuntu3
  Architecture: amd64
  CasperVersion: 1.367
  CurrentDesktop: MATE
  Date: Sun Mar 13 12:48:41 2016
  LiveMediaBuild: Ubuntu-MATE 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160224)
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: lvm2
  UpgradeStatus: No upgrade log present (probably fresh install)

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