Frank Campbell f_campbell at
Mon Feb 24 13:43:17 PST 1997

* From the SCSI Reflector (scsi at, posted by:
* Frank Campbell <f_campbell at>
Before we consider withdrawal of SBP we should subject SBP-2 to greater

There are aspects of SBP-2 which I believe should give rise to concern:

1.	SBP-2 requires that targets deal with scatter/gather and paging
issues within the host.
2.	SBP-2 requires that targets have the capability to break transfers up
on odd byte boundaries.
3.	SBP-2 uses host addresses as handles with no means of identifying
stale handles, exposing the risk of stale handles causing corruption.
4.	SBP-2 uses more bus transactions than necessary to perform I/O. As a
worst case example, a single sector read from disk requires up to 14 bus
arbitration cycles and 14 packet transfers.
5.	SBP-2 hosts use DMA addresses supplied by targets, creating security

Items 1,2 and 4 relate to the cost and complexity of target hardware and
firmware. Items 3 and 5 relate to reliability and security.

Frank Campbell
Qlogic Corporation
Costa Mesa, California.
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