ZFS scheduling

[Anselm Strauss]

Hi,

I noticed that my system gets very slow when I'm doing some simple but
intense ZFS operations. For example, I move about 20 Gigabytes of data
from one data set to another on the same pool, which is a RAIDZ of 3 500
GB SATA disks. The operations itself runs fast, but meanwhile other
things get really slow. E.g. opening a application takes 5 times as long
as before. Also simple operations like 'ls' stall for some seconds which
they did never before. It already changed a lot when I switched from
RAIDZ to a mirror with only 2 disks. Memory and CPU don't seem to be the
issue, I have a quad-core CPU and 8 GB RAM.

I can't get rid of the idea that this has something to do with
scheduling. The system is absolutely stable and fast. Somehow small I/O
operations on ZFS seem to have it very difficult to make it through when
other bigger ones are running. Maybe this has something to do with tuning?

I know my system information is very incomplete, and there could be a
lot of causes. But anybody knows if this could be an issue with ZFS itself?

Thanks,
Anselm