[Beowulf] Software RAID?

Mark Hahn hahn at mcmaster.ca
Thu Nov 22 18:33:10 EST 2007


just to tie up a loose end: HW raid controllers tend to cost $50-100/port
(areca/3ware, for instance - I'm sure there are many even more expensive.)
this probably sounds good to people used to the scsi/fc realm of prices,
but now consider: what is the price of the disk on that, say, $80 port?
currently, a 500G disk is $90 or so (pricewatch).

> 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.

sync workloads are funny.  often, it's really just someone equating 
paranoia with safety and thus goodness.  sometimes it can be easily 
designed around (for instance, suppose I log over a network to two 
independent (ups'ed) machines, and each keeps the log in normal system ram.)

but I think it will quickly become normal to use flash disks or 
flash-augmented disks to address this.
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