[Beowulf] Software RAID?

Mark Hahn hahn at mcmaster.ca
Wed Nov 21 20:19:19 EST 2007

> 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?

yes, MD, the standard Linux software raid, is generally faster 
than HW raid.  yes, this can be argued, though not in any kind 
of slam-dunk.  as far as I know, the very fastest HW raid (3ware 
and areca - I wouldn't guess LSI) top out at 6-800 MB/s.
obviously, MD will consume some cycles supporting that kind of 
bandwidth, but it can be done.

for a typical cost-sensitive fileserver, especially if only over 
a gigabit or two, MD is a no-brainer.  It Just Works and most any 
MB will already have ~6 sata ports, so you just plug in some 
disturbingly cheap 320-1000G sata disks (~60 MB/s each), and 
you're flying.

> With the availability multi-core chips and SSE instruction sets, it
> would seem to me that this is doable.

SW raid has generally been the right choice for 5+ years - 
since the host got fast memory interfaces, basically.
even the earliest MMX helped out with this stuff.  and the host 
CPU is always going to be many times faster than the little
embedded core on a HW raid card.

> Would be nice to not have to pay
> for those RAID cards if I don't have to. Just wondering if anything
> already exists.

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