On Dec 28, 2009, at 4:53 AM, Morten-Christian Bernson wrote:
The best place to start looking at disk-related
performance problems
is iostat.
Slow disks will show high service times. There are
many options, but I
usually use something like:
iostat -zxcnPT d 1
Ignore the first line. Look at the service times.
They should be
elow 10ms
for good performance.
Thanks for the reply!
It seems that c2t4d0s0 is the one making trouble, as I suspected.
Here is a sample line from the output while copying a file from the
DATA-pool to /tmp/:
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
17.0 6.0 896.5 8.5 0.7 27.6 31.8 1201.5 73 100 c2t4d0s0
The asvc_t is insanely high, while the other disks are from 0 to max
80, but mostly around 0.
Is someone yelling at it? :-)
But seriously, check the drive for vibration and if that doesn't fix
the performance, consider replacing it or the cables. 1.2 seconds
is just way too slow for an I/O request.
What does this mean? Is the disk defective? Could I get it
replaced by the warranty? If I want to exchange it in the pool with
the hot spare, how do I go around doing that? I want to make sure
that the whole pool doesn't collapse on me if I take out this disk,
and then the problems isn't really this disk but some other, and the
whole pool is gone...
With a 1.2 second response time, the entire pool will be really,
reaallllltyyyyy sllllllllllllllooooooooooooowwwwwwwwwwwwwww.
You should see something more like 10ms response time -- two
orders of magnitude better.
-- richard
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