RE: Miserable Disks
- From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
- To: <charlottejanehammond@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 23 May 2006 18:26:50 -0400
Charlotte,
Are you using raw volumes? Filesystem? If filesystem, which one?
-Mark
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Mark J. Bobak
Senior Oracle Architect
ProQuest Information & Learning
For a successful technology, reality must take precedence over public
relations, for Nature cannot be fooled. --Richard P. Feynman, 1918-1988
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Charlotte Hammond
Sent: Tuesday, May 23, 2006 12:54 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Miserable Disks
Dear All
I am struggling to get any sort of acceptable performance from our
storage array. It's a low end SATA RAID-5 (NOT my choice!) so I'd
expect performance to be poor but it's much worse than poor, it's
utterly diabolical. Apologies in advance for the long email full of
data but I really hope somebody might be able to spot what's gone wrong.
I'm on 9.2.0.6 running on RHEL4 Linux with async i/o compiled and
filesystemio_options=setall.
Asynchronous i/o is I believe enabled since the kio* figures in
/proc/slabinfo are non-zero.
Iostat shows (I think) the average write to be a mere
512 bytes (NOT kbytes) whilst importing lots of LOBs.
The aio-max-size parameter isn't available in RHEL4 so I can't try to
tweak it.
Here's a typical snapshot for iostat for a period of 2 seconds (this
will probably format horrible - sorry):
avg-cpu: %user %nice %sys %iowait %idle
0.64 0.00 0.13 8.71 90.52
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
rkB/s wkB/s avgrq-sz avgqu-sz await svctm
%util
sdc 0.00 39.18 76.29 35.05 1321.65 875.26
660.82 437.63 19.73 1.19 10.75 9.00
100.26
And here's some O/S call trace timing for a period of
2 minutes:
lseek: 0.00140
fcntl: 0.00143
setitimer: 0.00147
ftruncate: 0.00288
semctl: 0.00308
rt_sigprocmask: 0.00362
close: 0.00555
stat: 0.00620
open: 0.00821
read: 0.23854
getrusage: 0.41848
gettimeofday: 1.00980
semop: 3.30752
pwrite: 3.57569
io_submit: 4.15861
write: 6.48122
pread: 8.84140
fsync: 19.85780
io_getevents: 69.24410
The io_getevents system call only ever returns a value of 1.
Thank you!
Charlotte
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