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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