[Beowulf] GPFS on Linux (x86)

Mark Hahn hahn at physics.mcmaster.ca
Thu Sep 14 16:11:27 PDT 2006

> However, what if you know you need better access time or more reliable better 
> disks (SCSI is still more reliable than SATA in most cases) and want to 
> invest in 10k or 15k SCSI disks?

I'm not sure I've met anyone who really knew that 
rather than believing it on faith ;)

for instance, it's not trivial to argue better SCSI access time in 
an environment where you have many disks.  I suppose if you actually
have a _single_ thread of IO, you really will always only care about
the latency of that single outstanding op, but that seems pretty exotic.
striping handles multiple streams pretty nicely (even striped journal
devices, if you're doing massive updates...)

reliability is even fuzzier because vendors are such jerks about publishing 
their numbers.  in the broadest sense, the availability of 5-year warantee,
"raid-edition" SATA disks is kinda sorta equivalent to SCSI.  SCSI disks 
do sometimes include MTBF specs (1.0-1.4 Mhours, iirc) - SATA is probably
somewhere above 800K hours, though that's somewhat confounded by how you 
figure the working load (24x7, 8x5, temperature, etc).  and the lack of 
numbers from SATA vendors...

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