Re: Miserable Disks

Charlotte,

What exactly is slow? Why do you think it's the storage that's slow?

Looking at the numbers:

76 reads + 35 writes = 110 IOs/ sec with a queue of 1.2 is perfectly normal.
service time = 9 ms . (7200 rpm = 0.008333 ms rotation delay) so it's
typical for a "slow" drive. It's relativelly "normal" for 10k drive
given your load.

"avgrq-sz" is in sectors so 19.23 is 9.865 Kb average request size.

If you ask me, your storage is not performing badly. What did you
expect as numbers?

--
Christo Kutrovsky
Senior Database/System Administrator
The Pythian Group - www.pythian.com
I blog at http://www.pythian.com/blogs/

On 5/23/06, Charlotte Hammond <charlottejanehammond@xxxxxxxxx> wrote: 
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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--
Christo Kutrovsky
Senior Database/System Administrator
The Pythian Group - www.pythian.com
I blog at http://www.pythian.com/blogs/
--
http://www.freelists.org/webpage/oracle-l


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