[wplug] RAID performance

[Mike S]

Low and behold, I just got a 3ware 9650 yesterday, with 4x750 seagates.
We're mostly going to be doing linear reads from it anyway, so I'm not super
concerned with the performance.  I don't have a software RAID to compare it
to, sorry.  But, just for giggles, I'll try to do a little benchmarking on
it this afternoon.

However, the thing that sticks out in my mind about your test is the
difference in drives -- SATA I vs SATA II.  My impression was that SATA II
was a big improvement over SATA I.

I wonder if this could be the difference.  Also, to me, 24MB/s looks slow.
I have a 5x400GB Adaptec hardware RAID array that gets around 45MB/s, and
everything in there is at least two years old.  So, is it possible that
there's something else at play here?

On 3/2/07, Patrick Wagstrom <pwagstro at andrew.cmu.edu> wrote:
>
> 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
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