Hi, On Tue, 07 Apr 2009, Amos Jeffries wrote: > Gavin McCullagh wrote: >> Mine too. The operating system is on linux software RAID1 partitions so I > > Ah, there we probably have the answer as to why there is so much iowait. I'm not convinced of that. The iowait seems to grow directly as a function of the cache size and the caches themselves are not RAIDed. You can see that I recently reduced the cache size and got an immediate, substantial reduction in iowait. http://deathcab.gcd.ie/munin/gcd.ie/watcher.gcd.ie.html#Squid http://deathcab.gcd.ie/munin/gcd.ie/watcher.gcd.ie.html#System > You may want to find out how to determin RAID iowait vs other iowait and > see what shows up. That would be interesting alright. I'll see what I can find out. > Though I only had 2x 250GB disks on 2.6GHz box RAID1, Squid maxed out > and started seriously lagging requests under 3 users (at around ~5Mbps > wild guess). Did you have the cache on RAID1 or the OS or both? Hardware or software RAID (not that my using software should improve anything of course)? > I shifted to a *slower* 1.8GHz box with single OS-shared disk and it now > hits serves 15 users without sweating and runs dozens of reverse-proxy > domains as a side job. Squid's usage of CPU time doesn't seem to be an issue for us at all so I can well believe that. > My review of RAID + Squid was overruled by some RAID experts with more > experience. I'm still puzzled how they got the evidence for > "performance: quite good" on software RAID though, maybe dual-core > minimum, mine are both singles. I can certainly see how putting the cache on software RAID1 is a bad plan, but that's not what I've done and the iowait is sensitive to cache size. I have the squid logs and the squid cache on single disk partitions. I don't think the OS shouldn't be loading the disk too much. Many thanks for your help on this, Gavin
