On Aug 4, 2010, at 11:18 AM, Bob Friesenhahn wrote:
Assuming that your impressions are correct, are you sure that your
new disk drives are similar to the older ones? Are they an
identical model? Design trade-offs are now often resulting in
larger capacity drives with reduced performance.
Yes, the disks are the same, no problems there.
On Aug 4, 2010, at 2:11 PM, Bob Friesenhahn wrote:
On Wed, 4 Aug 2010, Eduardo Bragatto wrote:
Checking with iostat, I noticed the average wait time to be between
40ms and 50ms for all disks. Which doesn't seem too bad.
Actually, this is quite high. I would not expect such long wait
times except for when under extreme load such as a benchmark. If
the wait times are this long under normal use, then there is
something wrong.
That's a backup server, I usually have 10 rsync instances running
simultaneously so there's a lot of random disk access going on -- I
think that explains the high average time. Also, I recently enabled
graphing of the IOPS per disk (reading it using net-snmp) and I see
most disks are operating near their limit -- except for some disks
from the older VDEVs which is what I'm trying to address here.
However I did have CPU spikes at 100% where the kernel was taking
all cpu time.
I have reduced my zfs_arc_max parameter as it seemed the
applications were struggling for RAM and things are looking better
now
Odd. What type of applications are you running on this system? Are
applications running on the server competing with client accesses?
I noticed some of those rsync processes were using almost 1GB of RAM
each and the server has only 8GB. I started seeing the server swapping
a bit during the cpu spikes at 100%, so I figured it would be better
to cap ARC and leave some room for the rsync processes.
I will also start using rsync v3 to reduce the memory foot print, so I
might be able to give back some RAM to ARC, and I'm thinking maybe
going to 16GB RAM, as the pool is quite large and I'm sure more ARC
wouldn't hurt.
Thanks,
Eduardo Bragatto.
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