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Re: Hardware vs Software RAID 10 performance?

michael@estone.ca wrote:

Quoting Neil Gunton <neil@nilspace.com>:


(First of all, I apologise if anyone sees this twice - I first posted
to the AMD64 list, but then thought that the more general debian users
list might get a broader response)...

I'm curious as to whether anyone has experience of software RAID in
Linux giving better overall performance on RAID10 than a RAID card such
as the Adaptec 2015S.

Server: Debian Etch AMD64 on Dual Opteron 265, 1.8GHz, i.e. 4 cores
total, 4GB RAM, 4x10k Fujitsu SCSI 73GB, Adaptec 2015S zero-channel
RAID card.

Currently I have the four drives in RAID10 using the Adaptec, i.e. it
appears as one big drive to Linux. Then a few days ago I saw this video
presentation on scaling from one of the guys who developed YouTube:

http://video.google.com/videoplay?docid=-6304964351441328559


Does anybody have any experience of this, or wisdom to impart? I have
read all the arguments in favor of software RAID, and that's all very
nice, but what I am primarily wondering about here is if it's likely
that shifting over to software RAID might allow Linux to improve IO by
more parallelization of reads/writes, or if it's just shifting
complexity from one place to another, with the same bottleneck in
between? (In which case, I guess, might as well go with software RAID,
since it seems easier to recover from a controller crash).
I suppose your system is in production and you can't really down it and run some tests to see if one out performs the other?
It's not nearby, in a datacenter up in Chicago... I'm in St Louis currently. However I will be going up in mid September to re-install the system. I have about an hour in the datacenter (they charge me for access, since someone has to be with me). I would certainly like to do some tests, though I have found the output from bonnie++ somewhat inscrutable and hard to parse, and I don't have a good handle on what parameters to give these benchmarking programs to really test what I'm talking about. It would be nice to be able to have some pre-made tests ready to run quickly just to get an idea. However I probably won't have time for more than a couple of install cycles before I have to finalize and be out of there. 

Thanks,

/Neil
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