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_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