[TriLUG] lvm2 cache-pool backported to Ubuntu 14.04?

[Cristóbal Palmer via TriLUG]

Greetings LUG folks,

I have some developer workstations that have dev/test VMs on them, and we're
experiencing disk I/O that bogs these machines down whenever a workstation has
more than two guests. We are in the process of acquiring 128GB SSDs, and this
post is asking about a specific strategy for using those SSDs to speed up the
machines for our use case.

To simplify, let's say we have the following (close enough to the truth):

  $ sudo pvs
    PV         VG    Fmt  Attr PSize   PFree  
    /dev/md0   boot  lvm2 a--  900.00m 100.00m
    /dev/md1   knuth lvm2 a--  500.00g 120.00g
    /dev/sdc1  knuth lvm2 a--  115.38g  34.24g

and that /dev/md0 and /dev/md1 are a raid 1 array of two slow 500GB disks,
while /dev/sdc is the new SSD. What I'd like to do is use the cache-pool in
a manner something like Richard Jones and others discussed last year on the
linux-lvm list[0].

To that end, I've made two logical volumes:

  $ sudo lvs |grep cache
    lv_cache                     knuth -wi-a----  62.00g                                                                           
    lv_cache_meta                knuth -wi-a----  64.00m  

... and attempted to set them up as a cache pool:

  $ sudo lvconvert --type cache-pool \
  --poolmetadata knuth/lv_cache_meta knuth/lv_cache
    WARNING: Unrecognised segment type cache-pool

What some quick investigation makes clear is that my lvm2 is too old:

  $ dpkg -l lvm2 | grep ^ii
  ii  lvm2     2.02.98-6ubuntu2      amd64    Linux Logical Volume Manager

More searching shows some people willing to install lvm2 from source. We're
not an org where that's going to fly, and I'd rather not be in the business of
maintaining an lvm2 backport. Does anybody have experience getting this sort of
thing to work on Ubuntu 14.04? Did you for example use a backported package
from Vivid Vervet[1][2]? If so, what were your steps? How do you do maintenance
updates?

We have workstations running Debian 8.0, CentOS 7, Ubuntu 14.04 and CentOS 6.6,
so solutions that abandon Ubuntu are something I'm happy to see people write to
the list about, but remember that my priorities are such that using packages
that are easily pulled from a reputable upstream without needing to do a local
build are strongly preferred. I could hopefully have this working today if I
were willing to abandon that and just build lvm2 from source, but that possibly
sacrifices repeatability and maintainability for our office.

Cheers and thanks,
--
Cristóbal Palmer
ibiblio.org


[0] https://www.redhat.com/archives/linux-lvm/2014-May/msg00037.html
[1] https://launchpad.net/ubuntu/+source/lvm2
[2] https://launchpad.net/ubuntu/+source/lvm2/2.02.111-2ubuntu1