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Re: Hardware vs Software RAID 10 performance?

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?
Over the years, I've become more and more a fan of Software Raid. Especially since everything on the motherboard has gotten faster. I would be suprised if your adaptec controller out performed SW raid on the gear that you have, even when you system is under load.
Also, with SW raid, I get to have my hand on the pulse of it. The monitoring tools are nice and it will warn you if have a failed device by email.
If there any benchmarks out there on the web with SW vs HW raid, on newer systems, I would love to seem them. 

Cheers,
Mike
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