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

Chris Friesen chris.friesen at windriver.com
Mon Sep 14 18:46:00 UTC 2015

My apologies, I got the version wrong.  The tests below were actually from the 
3.4 kernel and LVM 2.2.95.   I'm doing tests on the newer versions now.


On 09/14/2015 12:05 PM, Chris Friesen wrote:
> 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
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