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On January 20, 2007 6:08:07 PM -0800 Richard Elling
<Richard.Elling@xxxxxxx> wrote:
Frank Cusack wrote:
On January 19, 2007 5:59:13 PM -0800 "David J. Orman"
<ormandj@xxxxxxxxxxxx> wrote:
card that supports SAS would be *ideal*,
Except that SAS support on Solaris is not very good.
One major problem is they treat it like scsi when instead they should
treat it like FC (or native SATA).
uhmm... SAS is serial attached SCSI, why wouldn't we treat it like SCSI?
On January 21, 2007 8:17:10 PM +1100 "James C. McPherson"
<James.McPherson@xxxxxxx> wrote:
Uh ... you do know that the second "S" in SAS stands for
"serial-attached SCSI", right?
Uh ... you do know that the SCSI part of SAS refers to the command
set, right? And not the physical topology and associated things.
(Please forgive any terminology errors, you know what I mean.)
That seems like saying, "Uh ... you do know that there is no SCSI in FC,
right?" (Yet FC is still SCSI.)
Would you please expand upon this, because I'm really interested
in what your thoughts are..... since I work on Sun's SAS driver :)
SAS is limited, by the Solaris driver, to 16 devices. Not even that,
it's limited to devices with SCSI id's 0-15, so if you have 16 drives
and they start at id 10, well you only get access to 6 of them.
But SAS doesn't even really have scsi target id's. It has WWN-like
identifiers. I guess HBAs do some kind of mapping but it's not
reliable and can change, and inspecting or hardcoding device->id
mappings requires changing settings in the card's BIOS/OF.
Also, the HBA may renumber devices. That can be a big problem.
It would be better to use the SASAddress the way the fibre channel
drivers use the WWN. Drives could still be mapped to scsi id's, but
it should be done by the Solaris driver, not the HBA. And when
multipathing the names should change like with FC.
That's one thing. The other is unreliability with many devices
attached. I've talked to others that have had this problem as well.
I offered to send my controller(s) and JBOD to Sun for testing, through
the support channel (I had a bug open on this for awhile), but they
didn't want it. I think it came down to the classic "we don't
sell that hardware" problem. The onboard SAS controllers (x4100, v215
etc) work fine due to the limited topology. I wonder how you fix
(hardcode) the scsi id's with those. Because you're not doing it
with a PCI card.
-frank
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