Miserable Disks

From: Charlotte Hammond <charlottejanehammond_at_yahoo.com>
Date: Tue, 23 May 2006 09:53:59 -0700 (PDT)
Message-ID: <20060523165400.81142.qmail@web34110.mail.mud.yahoo.com>

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

---

Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

--
http://www.freelists.org/webpage/oracle-l

Received on Tue May 23 2006 - 11:53:59 CDT