[wplug] RAID performance

[Patrick Wagstrom]

I'm in the process of speccing out a new machine for a research group 
here at CMU.  Needs to be fairly beefy, handle about 1TB of MySQL 
databases, plus room for other computations to take place.  Anyway, 
we'll put aside all the issues of MySQL and their choice of software, 
and instead focus on an interesting issue I noticed last night, and I'm 
looking for some help with it, or someone to double check it.

We've got a machine right now with 4x400GB Hitachi SATA I drives (model 
HDS724040KLSA80S) connected to a 3ware Escalade 9500S 4 port SATA RAID 
controller (128MB of ram on the controller).  These drives are 
structured in RAID 5.  And on the other hand, at home I've got 4x320GB 
Seagate SATA II (model STS3320620AS) running software raid 5 on a MSI 
K8N-Neo4 Platinum (8x SATA ports).  I went software RAID at home because 
of cost and because performance isn't overly critical for the home 
machine because it's just HDTV, which only needs about 2MB/s write speed 
max.

Anyway, I did some admittedly synthetic benchmarks to compare 
performance on the system because I wanted to get an idea how much the 
hardware RAID made a difference, or if we'd be better off getting an 
additional 2 or 3 500GB drives for the cost of the hardware RAID.  As a 
final point of comparison, I included my IBM T43p laptop which as a SATA 
harddrive inside and no RAID.  For read the speeds are averaged over 10 
runs of hdparm.  For writes the speed is averaged over 3 consecutive 
runs.  Here's what I found:

using hdparm -tT to get an idea of read speed:

9500S Hardware: 52MB/s
K8N Software: 178MB/s
T43p No Raid: 40MB/s

Then I decided to find some large files and copy them from one location 
on the drive to another.  This was the best I could do because I didn't 
want external drives to be the bottleneck and the hardware raid machine 
has all disks as part of the array:

9500S Hardware (1.5G file): 24MB/s
K8N Software (1.1G file): 42MB/s
T43p No Raid (2.3G file): 11.5MB/s

So, as should be expected the laptop lags behind on just about 
everything.  However, what I was surprised to find was that software 
RAID 5 destroyed the hardware RAID 5 in terms of speed.  This leads me 
to wonder about a few things and I'd like to get other peoples feedback.

Does anyone else have a 3ware 9500s running RAID 5 that they could 
provide some useful benchmarks from?  Are there tuning parameters I 
should enact on the 9500s to increase performance?  Should the switch 
between SATAI and SATAII drives really make that much of difference?  My 
impression is that while SATA II drives theoretically supported 3Gbps 
they really come nowhere close -- which is what my results show. 
However, going 3x as fast for reads and 2x as fast for writes on 
software RAID was quite surprising.

Any comments?

Thanks!

--Patrick