topic Re: iostat and high wait state in Operating System - Linux

iostat and high wait state

Colm O Cinnseala — Fri, 06 Jan 2006 10:28:56 GMT

Folks
I admin a site with a selection of proliant servers and an EVA SAN.

While doing some performance testing recently I noticed that the io wait state was up to 50%. The files on disk are OCFS. I am getting contrary advice. An Oracle guy says that this is totally unnaceptable. A HP system engineer says that this is not a problem. Anyone any views on it?

Thanks

Colm

Re: iostat and high wait state

Vipulinux — Fri, 06 Jan 2006 10:34:23 GMT

Hello

In general, a high iowait percentage indicates the system has a memory shortage or an inefficient I/O subsystem configuration. Understanding the I/O bottleneck and improving the efficiency of the I/O subsystem require more data than iostat can provide.

50% should be normal on a DB Server.

Thanks

Re: iostat and high wait state

Ivan Ferreira — Fri, 06 Jan 2006 13:33:03 GMT

How are you doing your testing? OCFS performance cannot be tested with operating system commands.

You can test the vdisk performance with hdparm -Tt.

Hight iowait could be a problem, on an installation, the iowait was reduced and performance increased by using raw devices instead of OCFS filesystem.