RE How can I make my HW RAID reads faster? (request for FAQ)

[Matthias Saou]

Cyrille Bollu wrote :

> I have a Perc5e with a MD1000.
> 
> In general,I find Perc's cards performance poor and I would be happy to 
> find a way to improve. So, I would gladly participate in this discussion.
> 
> How did you measure your read speed? Using hdparm? 

That's the first simple test you can do, yes. Changing the Linux
read-ahead setting for the block device will show you a big difference
in the hdparm results, since it's a simple (linear?) read. I get 600MB+
(PE1950, PERC5/E, MD1000 w/ 15 1GB SATAII drives). One thing I still
haven't really been able to explain in my hdparm results is why I get
much slower results when testing the partition I have instead of the
block device itself (sdb1 vs. sdb).

Once your hdparm tests will give acceptable results, you'll definitely
want to use some more advanced testing techniques. I've used :

- Simple dd, cp and cat to /dev/null on multiple huge files or
directories full of small files.
- Multiple simultaneous runs of the above for "concurrent" accesses.
- iozone for random reads and writes.

Always make sure that the tool you're using isn't using up 100% CPU on
one core, as this means that the throughput of the test is being
limited by CPU usage and no by disk I/O.

I wrote a (very) quick summary of my findings here :
http://thias.marmotte.net/archives/2008/01/05/Dell-PERC5E-and-MD1000-performance-tweaks.html

Mainly just to have it for myself the next time I install something
similar ;-)

Matthias

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