vinum performance

[Jan L. Peterson]

Just to shed some real-world light on this vinum benchmark discussion.  
At a previous employer we had a few HP systems with hardware RAID 
boards on them (AMI MegaRaid compatible boards, but some HP part 
number... I can't remember exactly which).

On one system, which was in support of our web site (it stored 
thousands of small files containing html text that would be referenced 
in pretty much random order), we configured an HP RS12 (JBOD with 12 
disks in it) on the AMI controller as a RAID 5 volume.  Performance was 
excellent (this disk supported mostly reads... once a collection of 
files had been uploaded, it was not modified).  Much better then with 
the files on local disk, even.

On another system, where these files were created before being 
uploaded, performance with RAID 5 was abysmal.  We ended up yanking the 
AMI controller and using the on-board Symbios controller and using 
vinum as RAID 0+1 (stripe each group of six disks, mirror one group to 
the other group, each group on a separate physical controller -- the 
Sym board had dual channels).  With this setup, performance was much 
better.

So the upshot is, if you're doing a lot of writes, don't use RAID 5.  
If you're doing a lot of reads, and you have hardware RAID 5 available, 
it's probably a win.

	-jan-
-- 
Jan L. Peterson
<jlp at softhome.net>
If your company is looking for a SAGE level IV, let me know.