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Re: Miserable Disks

From: Christo Kutrovsky <kutrovsky.oracle_at_gmail.com>
Date: Wed, 31 May 2006 17:29:51 -0400
Message-ID: <52a152eb0605311429u50aebc48p456f86786405ff78@mail.gmail.com>


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_at_yahoo.com> 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
Received on Wed May 31 2006 - 16:29:51 CDT

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