[Beowulf] Software RAID?

Jakob Oestergaard jakob at unthought.net
Thu Nov 22 09:49:07 EST 2007


On Wed, Nov 21, 2007 at 03:18:43PM -0800, Ekechi Nwokah wrote:
> Hi,
> 
> Does anyone know of any software RAID solutions that come close to the
> performance of a commodity RAID card such as LSI/3ware/Areca for
> direct-attached drives?

Others have already presented pretty good descriptions of the pros and cons of
SW-in-the-main-processor (AKA SW RAID) versus SW-in-a-smaller-addon-processor
(AKA HW RAID).

One thing that HW RAID has, though, that SW RAID fundamentally cannot get, is a
battery backed write cache. This can, for many workloads, prove to give a very
significant performance advantage (for sync heavy workloads you can get several
orders of magnitude speedup).  For other workloads it won't matter, of course.

...
> With the availability multi-core chips and SSE instruction sets, it
> would seem to me that this is doable. Would be nice to not have to pay
> for those RAID cards if I don't have to. Just wondering if anything
> already exists.

CPU speed hasn't mattered for SW RAID the past decade. Really. Not for RAID-1,
and not for RAID-5.

-- 

 / jakob

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