RAID Cards performance issue

[Christopher Chan]

Scott Balneaves wrote:
> On Fri, Dec 05, 2008 at 12:24:49PM -0500, Nicolas Roussi wrote:
>> Hi, I know that this topic is not the main subject matter of this list but I
>> was wondering if anyone has any experience with RAID adapters and
>> performance issues. I have already posted something on ubuntuforums.org (
>> http://ubuntuforums.org/showthread.php?t=1001858). I would appreciate any
>> input as to why the read speed on a 3ware 9650 RAID 5 would only be ~3MB/s
>> and a PERC5 would be 10 times that much. Is there a way to troubleshoot this
>> or maybe another benchmark for read and write speeds of my arrays?

Are you running the latest firmware from 3ware?

> 
> Raid 5's terrible at a lot of things.  RAID5's essentially a huge compromise,
> and doesn't really do ANYTHING well.  See:
> http://en.wikipedia.org/wiki/RAID5#RAID_5

Software raid5 get performance penalties but a hardware raid card with 
sufficient cache memory (must be battery backed if you want to minimize 
data loss) and processing power can do raid5 and perform as well as or 
even better than raid10 depending on the number of drives involved.

> 
> You'd be far, FAR better off with something like RAID0, or RAID10.  You lose
> half your drive space, but drives are cheap, and the performance gains are
> huge.
> 

RAID0? The guy has lost one drive already and you tell him RAID0 as a 
choice for performance? Even if I don't care about the data, I would not 
want to go through the trouble of replacing and recreating the array 
everytime a disk decides it does not want to play anymore.