Guy Boisvert boisvert.guy@videotron.ca writes:
Your %iowait seems high.
I had %iowait comparable to you with a single 200 Gigs 7200 RPM IDE drive.
Now we've upgraded this server: Opteron 2216 with 4 Gigs RAM, CentOS 64 v5.2) and an Adaptec 3405 plus 4 x 73 Gigs Seagate 15K RPM (RAID 10). No more %iowait! I benched it at about 140 MB/s and random r/w are very good on these drives.
Yeah. without dangerous write-back caching, as far as performance (as opposed to space) goes, expensive SAS disks (or even the expensive 15K sata disks) will get you a lot more than any amount of RAID on the cheap 7500RPM sata disks.
Really, once you have the 15K disks, I'm sure a mirror would be fine, if 73G is enough.
The new (and really expensive) solid-state flash drives are also really good for reducing your iowait.
The other thing to check is vmstat- if you have lots of si and so, well, your disk is slow 'cause you are swapping a lot. add more ram and the problem goes away.