[linux-lvm] Any way to speed up activation of volumes with snapshots?

[Chris Friesen <chris.friesen@windriver.com>]

Hi,

I'm running a 3.10 kernel with LVM 2.02.95.

I'm running into a problem where activating snapshots can take quite a long 
time, roughly one minute per 25GB of delta between the snapshot and the origin 
volume.  (See below for my test procedure.)

I realize that my kernel/LVM aren't exactly bleeding edge, and I wondering 
whether more recent versions have done anything to speed up the activation 
process (like maybe making it more lazy-loaded rather than reading in a bunch of 
data up-front).

If anyone is aware of such improvements, I'd appreciate it if you could point me 
at the appropriate changes.


For those that are interested, the test that I did was as follows:

lvcreate -L100G  -n test1 vg
lvcreate -L 100G -s -n test1snapshot /dev/vg/test1
dd if=/dev/zero of=/dev/cinder-volumes/test1snapshot bs=1M count=95000
lvchange -an  /dev/cinder-volumes/test1snapshot
time lvchange -ay  /dev/cinder-volumes/test1snapshot

The final "lvchange" command took about 4m22s.  This works out to 362MB/sec, 
which is almost exactly the speed I got doing a "dd" from the volume to /dev/null.

Thanks,
Chris