Mark Hahn wrote:
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...)
Fair comment. I wouldn't be the one buying the 15K scsi disks unless
it was proven they are that much faster for my application. I have
heard some horror stories about SATA disk in raid systems and how
vendors have to work around quirks in the SATA disks to get them to
work ok. They describe it as the SATA disks go 'out to lunch'
occasionally and a disk will have a large pause before continuing.
Those comments come from a vendor (Be wary).
But if my customer wants 15K disks, I am going to get them for him/her.
I am not going put the effort in convincing them to go with SATA. You
pick your battles even when serving them.
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...
Large SATA array vs. Large SCSI array, same vendor. It appears that the
SCSI disks were a bit more reliable. I wish I had more numbers to
back it up, but that is what it seemed like. I don't buy any of the vendor
numbers.
Craig
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