> We are starting to see a number of SAS HDDs that prefer logical-block to
> round-robin. I see this with late model Seagate and Toshiba HDDs.
> There is another, similar issue with recognition of multipathing by the
> scsi_vhci driver. Both of these are being tracked as
> issues/644 and there is an alternate scsi_vhci.conf file posted in that
> bugid.

Interesting, I just last week had a Toshiba come from Dell as a replacement
for a Seagate 2TB SAS drive;  On Solaris-10, the Toshiba insisted on showing
up as 2 drives, so mpxio was not recognizing it.  Fortunately I was able to
swap the drive for a Seagate, but I'll stash away a copy of the scsi_vhci.conf
entry for the future.

> We're considering making logical-block the default (as in above bugid) and we
> have not discovered a reason to keep round-robin. If you know of any reason
> why round-robin is useful, please add to the bugid. 

Should be fine.  When I first ran into this a couple years ago, I did a
lot of tests and found logical-block to be slower than "none" (with those
Seagate 2TB SAS drives in Dell MD1200's), but not a whole lot slower.
I vaguely recall that round-robin was better for highly random, small I/O 
(IOPS-intensive) workloads.

I got the best results by manually load-balancing half the drives to one
path and half the drives to the other path.  But I decided it was not
worth the effort.  Maybe if there was a way to automatically do that
(with a relatively static result)....  Of course, this was all tested
on Solaris-10, so your mileage may vary.



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