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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