RE: Miserable Disks

From: Bobak, Mark <Mark.Bobak_at_il.proquest.com>
Date: Tue, 23 May 2006 18:26:50 -0400
Message-ID: <AA29A27627F842409E1D18FB19CDCF27080F7C1E@AABO-EXCHANGE02.bos.il.pqe>

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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Charlotte Hammond Sent: Tuesday, May 23, 2006 12:54 PM
To: oracle-l_at_freelists.org
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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http://www.freelists.org/webpage/oracle-l Received on Tue May 23 2006 - 17:26:50 CDT