Ongoing U320 AIC7902 Seagate ST318453LW issues, SCB timed out

Justin T. Gibbs gibbs at
Mon Aug 11 10:59:49 PDT 2003

> So i've reconfirmed, the drive supports a max of 64 tags.
> under load I see the max go down to 252, how can that make
> sense? under severe load it may go lower, to e.g. 33.

The actual number of transactions these drives support depends
heavily on load.  For reads, I believe that you can have much
more than 64 commands outstanding to this drive.  Once you start
to fill the write buffer, the number of commands the drive can
hold drops to 32 or 33 depending on the firmware rev.  It seems
that command resources are managed dynamically and that deferrred
writes hold on to those resources while they are draining to
the media.


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