[CentOS] RAID on Email Server

Luke S Crawford lsc at prgmr.com
Tue Oct 21 00:43:26 UTC 2008


Guy Boisvert <boisvert.guy at 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. 


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