[Beowulf] SATA vs SCSI drives

Mark Hahn hahn at physics.mcmaster.ca
Mon Oct 11 13:23:15 EDT 2004


> imaging and data acq. systems. Reliability for storage of this data is
> a big time must.

good - reliability is easy.  the ubiquity of raid has made inherent
drive reliability less of a critical factor.

> To date, we have built all of this lab's gear around SCSI drives because it
> has been our research and experience that SCSI drives are better built
> than IDE drives.

research = web opinions?  there are some differences between traditional
scsi products and everything else.  I don't think most customers, even 
ones who've tried to inform themselves, understand what the differences 
really are.

basically, SCSI is and has always been driven by "enterprise" database 
needs.  for instance, higher RPM is not a way to get higher bandwidth -
indeed, higher density, lower-RPM disks often deliver higher bandwidth,
and in any case, bandwidth is easily scaled by striping.  the real
differences have more to do with expected duty cycle and lifespan.
again, the enterprise DB market expect to be able to do max seeks/second
for the full service life, 24x365.2425x5.

your use almost certainly does not involve constant, maxed-out activity.
as such, your solution should not use parts designed and priced for that.

> However, when looking at these drive arrays and NAS
> appliances, it is very clear that SATA drives are really driving large scale
> storage.

enterprise DB's are not driven by density, whereas the rest of the market is.
there are good technical reasons for this divergence (more heads means slower
seeks; greater density means slower seeks).

> What has been the general experience on this list of SATA vs SCSI in terms
> of performance, reliability, quoted as well as real-world failure rates, 
> etc?

somewhat higher infant mortality due to a lower-quality supply chain for 
low-end (*ata) disks.  in use, failure rates more or less in keeping with
the drives mtbf or warranty.

> Which SATA drives are considered 'the best' the way, say Seagate drives are
> held in high esteem for SCSI?

your statement about Seagate is pure aesthetics, and I very much doubt that 
there's a clear taste preference for Seagate.  (for instance Fujitsu, HGST
and Maxtor all make drives of equal quality/reliability/performance.)

> And, if anybody likes any particular RAID and/or NAS system, let's hear
> your stories. About 1.4-1.7 Terabyte raw space.

small servers like this are no longer much of a challenge or interest.
just slap 8x250G sata disks into a box, raid5 with one hot spare, and relax.
personally, I'm fond of Promise s150tx4 controllers since they're cheap
and effective.  any 3-5yr warranty disk from seagate/maxtor/hgst/wd will
work perfectly fine.  yes, of course the box should have decent airflow,
and a hefty power supply, but none of that is hard anymore (it also helps
that disks themselves have become cooler.)

regards, mark hahn.

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