FAQ
Hi, list friends;

I have question about disk io performance, would like to hear from your
experience.

We have a HDS 9570 in production, it consists of two box, two
controller, and 2GB Cache per controller. 14 hard disks per box. We build a
RAID10 on each box with 6D+6P and 2 hotspare.

Response time is good, as iostat -xn shows the response time is between
3-5 ms.

But IO wait seems pretty high, with only 600IO per second, we are seeing
15+% io wait(sar -u 60 60). Server is Sun Fire V880 with 8CPU and 16G
memory, running oracle database server. Database also runs on vxfs
filesystem without quickio.

extended device statistics

r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
388.9 135.8 3228.0 1204.0 0.0 2.1 0.0 4.0 0 81
c3t50060E8000439AA0d2 --HDS lun, consists of 12 hard disks.Raid10.one box.

0.0 72.8 0.0 275.3 0.0 0.0 0.0 0.5 0 2
c3t50060E8000439AA0d1 --Same HDS Lun.spit into two diskgroups
350.1 103.8 2876.9 905.6 0.0 1.8 0.0 3.9 0 79
c3t50060E8000439AA0d2

0.0 48.8 0.0 210.2 0.0 0.0 0.0 0.5 0 1
c3t50060E8000439AA0d1

While on the similar server, with only 2 disks in a veritas diskgroup, I
created a striped volume and filesystem on this volume, I can do 1200IO per
second.(iostat -xn 60), though response time is quite high(60-90ms), this
server runs test database.

extended device statistics

r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
683.5 0.0 42339.2 0.0 0.2 41.1 0.2 60.2 6 100 c1t3d0
671.5 0.5 42971.2 4.0 31.9 64.0 47.5 95.2 98 100 c1t4d0
A single internal disk can do around 700 read per second.

So my question is:
with 12 disks and 2gb cache, Why does the solaris show 15+% iowait with only
600IO per second? Shall I pay attention to this iowait? Is there any special
configuration that we should make?
How about your external storage? (IOPS, number of disks, and raid level).

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postedMay 17, '04 at 9:07a
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