[linux-lvm] advice for curing terrible snapshot performance?
chris (fool) mccraw
gently at gmail.com
Sat Nov 13 00:17:58 UTC 2010
On Fri, Nov 12, 2010 at 15:36, Joe Pruett <joey at q7.com> wrote:
> i just did a bit of poking around and discovered that snapshots have
> their own chunk size that is used for the copy on write magic.
indeed. i was hoping someone would advise me if there was a better
chunk size, which is why i said what i thought i was using (default =
64k) in my first post.
> and it
> defaults to 4k, and you can only increase that to 512k. a simple test
> of creating a 1g file went from 240mbytes/sec to 4mbytes/sec with 4k
> chunk, and 12mbytes/sec with 512k chunk. so i'm not sure what the
> bottleneck is, but is surely is there.
interestingly the default snapshot chunk size on my system:
LVM version: 2.02.56(1)-RHEL5 (2010-04-22)
Library version: 1.02.39-RHEL5 (2010-04-22)
Driver version: 4.11.5
is 4k. a tutorial i was reading suggested it was 64k, and i didn't
doublecheck if that was true. i am going to have to wait til after
business hours to run more thorough tests, but i still see a slowdown
way over 10x even at 64k chunk size with a single snapshot. i'll try
it at all the different available chunk sizes and report back by
still curious about Zumastor--does anyone use this in production?
More information about the linux-lvm