Bi-Directional Commands.

Robert Snively rsnively at Brocade.COM
Mon Jan 22 08:12:52 PST 2001

* From the T10 Reflector (t10 at, posted by:
* Robert Snively <rsnively at>
Dear Santosh,

To answer your questions:

	The intent of the BI-DI commands is to have one SCSI Status
	and one SCSI Sense for the entire operation.  

	The commands are incomplete unless both the requested outbound
	transfer and the requested inbound transfer are completed.

	If there is a requirement for separate inbound and outbound
	status to be maintained, the function should be architected as
	two separate commands.

	The status and sense information has not yet been defined for
	the commands.  I assume that the necessary information to describe
	a failure will be provided by the commands.  Note that the
	protocols are likely to provide separate length residues for
	both inbound and outbound data, but that information is not
	meaningful outside the context of a particular command.

Bob Snively

Bob Snively                        e-mail:    rsnively at
Brocade Communications Systems     phone:  408 487 8135
1745 Technology Drive
San Jose, CA 95110

-----Original Message-----
From: Santosh Rao [mailto:santoshr at]
Sent: Tuesday, January 16, 2001 3:49 PM
To: T10 Reflector
Subject: Bi-Directional Commands.


I have a question regarding the new BI-DI commands and its related
changes that were proposed to SAM-2, SBC-2 (XDWRITEREAD), and the SPI-4,
FCP-3 and iSCSI SCSI Transport protocols.

Was the BI-DI type of operation only intended to be used in a XOR type
I/O (ex: XDWRITEREAD) like a READ-WRITE or WRITE-READ of the same (LBA,
count) ? i.e. Is there an inherent assumption that BI-DI operations will
always result in a single SCSI Status and SCSI Sense for the entire
operation, as opposed to potential individual SCSI Status or Sense for
either the inbound or outbound operation.

Is there a possibility that different SCSI Status or Sense may need to
be returned for the outbound or the inbound portion of the BI-DI
operation rather than the current single status/sense model used in
Response IUs/PDUs ?

Are there any indications that a returned Status or Sense refer to the
outbound or the inbound portion of the exchange ?

Santosh Rao

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