topic Excessive i/o wait in Operating System - Linux

Excessive i/o wait

Sherbert Punt — Wed, 01 Jul 2009 09:11:00 GMT

Greetings

I have an oracle box that yesterday when in very high i/o wait on the / partition oracle has seperate partitions

iostat and sar confirmed that yes there was high usage on the disk

There were no backups nor unexpected processes running I turned off hpasm and our monitoring software but no joy...

I suppose my question is how does one locate the culprit that caused this...

Thanking you

Re: Excessive i/o wait

Steven E. Protter — Wed, 01 Jul 2009 09:56:01 GMT

Shalom,

I would stop and start the oracle database.

First place I would look would be at the database.

One ugly user interactive sql statement can be the cause of this.

Poor database layout could be it.

Its a fishing expedition. Take a look at disk layout. Look for index and rollback an data being on a raid 5 and being write intensive.

Look for hardware issues with the disk.

Keep looking until you find a cause.

SEP

Re: Excessive i/o wait

Goran Koruga — Wed, 01 Jul 2009 11:15:26 GMT

Hi.

To find out which process is responsible for I/O you can use two methods:

1. Use blktrace tools (needs CONFIG_BLK_DEV_IO_TRACE kernel option)

2. Use block_dump method, explained in kernel docs (laptop-mode.txt) - turn off syslog etc. before enabling this.

Regards,
Goran

Re: Excessive i/o wait

Sherbert Punt — Wed, 01 Jul 2009 12:19:43 GMT

Many thanks I shall test that out...

--Sherbert