At 13:53, on May 6, 2005, markallen(a)micron.com wrote:
>
> I'm investigating a performance problem with snapmirror and disrupting
> production services on my FAS980C. I've seen it impact both NFS and
> CIFS. The filer becomes unresponsive for 30s to 1 minute when a
> snapmirror process kicks off. The snapmirror process is actually on the
> destination end of the process so it is pulling the data from another
> FAS980. I'm running 7.0.0.1 on a raid 4 traditional volume with 50
> spindles in the volume. My cpu's and memory are far from exceeding max
> capacity. Anybody have a clue as to what could be causing this?
Snapmirrors force a lot of disk write IO, and hence a lot of CPs.
That's both when when a snapshot is created, and even more when a
snapshot is deleted.
If your filers do a lot of writes in general, then you might be maxing
out CP. When you reach the state of being in back-to-back CP's, then
the filer starts not honoring Read requests, so that it can finish
flushing its writes.
Run "sysstat -u 1" and watch the CP columns. I'd bet that during the
problem, you'll see that you're in CP continuously, and that you end up
seeing #'s or B's in the CP type column.
(I'm speaking for ONTAP 6.4.x - but I don't expect that this has changed
much in 7.x.)
Davin.