Third-party SCSI data transfers

Lansing J Sloan ljsloan at anduin.ocf.llnl.gov
Mon Sep 19 16:03:35 PDT 1994


SCSI Folks,

Our proposal for third-party SCSI data transfers, e-mailed September
9, included three alternative possible approaches, each of which
appears to require changes in peripheral behavior.  At least two appear
to require changes in the content of SCSI control info.  Therefore
the proposal is directed to more than Operating System people.

The proposal is aimed mainly at high-performance access to mass
storage systems, as supported in the High Performance Storage
System (being developed jointly by IBM and several national
laboratories) and in the commercial product NSL-UNITREE.
Storage systems are responsible for the integrity of, say, file
systems.  They do not give client systems the power to damage that
integrity.  However, they do allow data transfers directly between
storage system devices and client systems in safe ways (provided
that the device and client support such transfers).

If such storage systems (based on the IEEE Mass Storage System
Reference Model) become widely used, we expect most "third-party"
traffic to be directly between devices and client processors,
with storage system controllers acting in some way to ensure only
safe transfers occur.  The three parties are the client processor,
the storage system controller, and the device.  This use of the term
"third-party" may not match exactly the current SCSI usage,
though one of the three approaches is based upon the COPY command.
I regret any confusion I may have created.

We don't know of any SCSI peripherals that support third party
transfers in the way NSL-Unitree and HPSS use them.  We've heard a
proposal and expect a market to develop, though.



> Date:         Thu Sep 15 06:32:23 1994
> From: Gene Milligan <Gene_Milligan at notes.seagate.com>
> Message-Id: <2e7822b8.seagate at notes.seagate.com>
> Organization: Seagate Technology
> Reply-To: Gene Milligan <Gene_Milligan at notes.seagate.com>
> To: SCSI at wichitaks.ncr.com
> Subject:      Re: Third-party SCSI data transfers

> I assume the proposal is directed to the Operating System people. Is this
> correct? If so, I imagine the CAM folks would need to deal with it. Keep in
> mind, it would be difficult to find any SCSI peripherals which implement
> third-party transfers except removable devices since it is targeted at backup
> applications. But I haven't followed this to understand why it falls under
> "third party".
> --
> Gene Milligan -- Gene_Milligan at notes.seagate.com
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