AHA2790UW has speed-limit problems ?

[Matti Aarnio]

Hello,

  Some days ago I sent a plea for fix to <linux-scsi at vger.rutgers.edu>
list.  As it turns out, my problem seem to relate on the chassis internal
ultra-wide cable, and to the devices attached to it.

Even the lattest beta (5.1.0-*) sequencer and associated code apparently
can not fix marginally working hardware.  (  :-|  )

The symptoms:

  Four Ultra-Wide (SingleEnded) disks on high quality cable inside
DEC PWS 433a workstation chassis attached to AHA2940UW host adapter.
The host adapter has termination configured (Active LOW, active HIGH),
and the other end of the cable has an active terminator for it.

Generating a load-set at which all disks (at least two) are actively
written at the same time seems to cause SCSI-bus timeouts IF the channel
is being run at the fastest mode.


The Kludge-Cure:

  Lower the speed of the device in the adapter bios configuration
utility.  In fact lower them all, and no SCSI-timeout problems appear.

Question:

  Is there ANYTHING that is possible to do to in this type of environment
so that I could (reliably) run faster disk-transfer speeds ?
Now my RAID0 write throughput has dropped from 12.odd MB/sec to 7.odd
MB/sec speed.

/Matti Aarnio 

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