[wplug] RAID performance

[Michael Skowvron]

Patrick,

On software vs. hardware RAID:
Software RAID benchmarks higher than hardware RAID because you tend to 
have all CPU resources available for the RAID calculations during the 
test. On a heavily loaded system, software RAID could end up having a 
big impact on system performance because the software RAID calculations 
compete with other tasks for CPU resources. So, hardware RAID may be 
slower, but it will be consistent performance regardless of system load.

For comparison, my 3Ware 7500 using 4x250GB PATA drives in a RAID5:

Write:
bfs:~/lmbench2/bin/i686-pc-linux-gnu # ./lmdd of=/safe/lmddtest move=1g 
sync=1
1073.7418 MB in 26.7281 secs, 40.1728 MB/sec

Read:
bfs:~/lmbench2/bin/i686-pc-linux-gnu # ./lmdd if=/safe/lmddtest
1073.7418 MB in 12.0338 secs, 89.2270 MB/sec

Your 9500 series should outperform my old 7500 series. BUT.... I was 
using null buffers to and from the device. Your test was to copy a large 
file from one place to another on the same device which tests 
simultaneous read-write.

Here's what I get for simultaneous read-write:
bfs:~/lmbench2/bin/i686-pc-linux-gnu # ./lmdd if=/safe/lmddtest 
of=/safe/copy sync=1
1073.7418 MB in 44.5771 secs, 24.0873 MB/sec



What stripe size did you use when you made the RAID5 volume?

Did the RAID complete the initial bind before doing your performance test?

Also, keep in mind that you are testing streaming reads and writes and 
you plan to use the unit for random access database queries. Latency on 
small I/O will be more important to your MySQL performance.

Can you download and compile lmbench, repeat these same tests, and 
report the results?

Michael


Patrick Wagstrom 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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