Hi Jack, > questions: > > 1) is top a valid measure of IO wait?
In my opinion sar is a better tool to look at IO waits. sar -d and sar -b will give you information on how the disk activity and I/O is. > 2) Is a high io wait an issue to be concerned about? Here is a nice note from Dave Miller with regards to Solaris though Just a note on iowait. On any multi-cpu machine, this number is not very useful, especially before Solaris 8. The algorithm for calculating it was changed in Solaris 8 but still is not really helpful. Prior to Solaris 8, iowait was defined as follows. When the scheduler attempted to schedule a process on a cpu, if there were no tasks that were runnable, but any task was marked as waiting for I/O, instead of counting as idle it counted as iowait. The problem on multi-cpu systems is that a single process waiting on I/O could count as iowait on ALL otherwise idle cpus. With Solaris 8 that was scaled down a bit (I don't have the exact details in front of me), but still is a bad gauge of I/O problems. I nearly always consider iowait to just be idle time and look for I/O problems elsewhere, like looking at iostat and looking at the %busy and service times on individual disks. That's much more indicative of a real problem and also will help you find out if you're hot-spotting on any disks. You also can monitor your networks using netstat because I believe iowait gets counted on processes waiting for network I/O, too. > 3) how else can it be accurately measured? sar I think gives a good idea > 4) How can I link IO wait to what is happening inside > the database? I think v$filestat will be the starting link. Hope this helps. Regards, Madhavan http://www.dpapps.com -- Madhavan Amruthur DecisionPoint Applications -- Please don't use http://fastmail.fm (I like feeling special.) -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Madhavan Amruthur INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
