Some thoughts on the previous data:
1. With devstack running it is likely that some portions of the 1G memory are
used by executables.
2. Having the VG on a loop mounted file can add some overhead on the IO as
everything has to
go trhough an additional layer and it is not guaranteed that consecutive
blocks of the loop
block device map to sequential blocks in the file system. That could make
merges harder.
3. I am not sure whether for the Virtualbox VM a paravirtual device driver
exists or whether block
devices are presented through an emulated controller (often PIIX). Compared
to the paravirt
driven block devices I use, the emulated devices are much slower.
4. Another factor that is often causing problems is that with 12.04, the
default IO scheduler changed
from deadline to cfq. It might be worth a try to set "elevator=deadline" in
the kernel command
line.
Looking at this, this could be a combination of slower block devices and
memory pressure and possibly some other event that causes problems for
the kernel tread that has to maintain a valid exception table on disk
while writing the zero blocks. At least this causes non-sequential
access patterns as the exception table is somewhere at the start of the
snapshot COW. As those need to be synchronized, this would explain why
erasing the snapshot takes much longer.
Next I would try to force the Xen guest to use emulated devices.
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1023755
Title:
Precise kernel locks up while dd to /dev/mapper files > 1Gb (was:
Unable to delete volume)
To manage notifications about this bug go to:
https://bugs.launchpad.net/cinder/+bug/1023755/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
