VME-SCSI adapaters

[Chris Johnson]

In article <9245 at brazos.Rice.edu> lindy!romeo at lindy.stanford.edu (Patrick Goebel) writes:
>X-Sun-Spots-Digest: Volume 9, Issue 232, message 7
>
>I understand that it is possible to buy a VME-SCSI adapter (e.g.  Ciprico
>Rimfire 3523) that allows the use of SCSI disks on the VME bus.  Several
>questions come to mind.
>
>1. Can I be assured that such an arrangement places no extra load on the
>   host SCSI bus?

What "host SCSI bus" are you referring to?  Connecting several SCSI disks
to a SCSI bus which is driven by a Rimfire 3523 (or any other SCSI host
bus adapter) is only going to directly affect that specific SCSI bus, not
any other SCSI busses you may have additionally connected to your system.
Of course, any VME bus activity, as well as any operating system activity,
necessary to actually do anything useful with those disks is going to
affect your over-all system performance, but that's true of everything you
might connect to your system.

>2. Are multiple SCSI devices simply daisy-chained off the VME-SCSI
>   adapter?

Essentially, yes.  SCSI is a bus architecture interface, in other words, a
daisy chain.  You can have up to 8 targets on a SCSI bus, which will
typically translate into 8 devices, where the host bus adapter always
counts as one.

>3. Given the relatively high transfer rates of synchronous SCSI (5
>   Mbyte/s) and the much lower cost of SCSI versus SMD or IPI, do people
>   consider this option a viable alternative to the more sophisticated
>   disk/controller technologies?

Many people do consider it viable.  It might even be a majority.  But for
truly high performance (and a commensurate high cost), SMD and IPI disks
and controllers will out perform SCSI.

   ...Chris Johnson          chris at c2s.mn.org   ..uunet!bungia!com50!chris
 Com Squared Systems, Inc.   St. Paul, MN USA   +1 612 452 9522