[Discuss] SAS drives

[dsr at tao.merseine.nu (Dan Ritter)]

On Wed, Aug 03, 2011 at 02:22:56PM -0400, Daniel Feenberg wrote:
> 
> 
> On Wed, 3 Aug 2011, Dan Ritter wrote:
> 
> >On Wed, Aug 03, 2011 at 11:09:09AM -0400, Daniel Feenberg wrote:
> >>
> >>
> >>On Wed, 3 Aug 2011, Dan Ritter wrote:
> >>
> >>>On Wed, Aug 03, 2011 at 10:05:55AM -0400, Edward Ned Harvey wrote:
> >>>>>From: discuss-bounces+blu=nedharvey.com at blu.org [mailto:discuss-
> >>>>>bounces+blu=nedharvey.com at blu.org] On Behalf Of Dan Ritter
> >>>>>
> >>>>>This is bizarre. SATA and SAS use the same cabling,
> >>>>
> >>>>Sometimes true, sometimes not.
> >>>>I have a Sun server X4275 which has a mixture of SATA and SAS drives in it.
> >>>>No problem.
> >>>>Later I bought an Oracle server X4270 (yes, the later model has a lower
> >>>>number, go figure.)  It has only SAS drives, and the connector is different.
> >>>
> >>>Can you describe the connector? And is it on the drives, or on a
> >>>backplane?
> >>
> >>In my case the socket on the drive has a bit of plastic that
> >>prevents an ordinary SATA cable from plugging in. The drives are
> >>Seagates. It does look to me like a cable connector could be
> >>constructed that would work in both types of drives, but none of the
> >>various SATA cables I have are so constructed.
> >
> >Oh, OK. Yes, SAS controllers can talk to SAS or SATA drives, but
> >SAS drives have a block so that only SAS controllers can talk to
> >them.
> 
> How effective is this block? It makes you get a special SAS cable to
> plug into the drive, but doesn't the controller end of the special
> cable plug into either a SAS or SATA controller? After all, the SAS
> controller port has to accept either cable, because it always
> supports both types of drives.

Not very effective, no. It's largely a product differentiator,
which is aggravating, as the SAS performance difference is
usually swamped by the controller's cleverness and cache.

-dsr-


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