Quantum tape drives will reject an SRR that does not specify the Relative Offset of the last XFER_RDY that we have sent for the exchange in question. This may or may not match the Relative Offset value in the last REC response (see 06-326r0 for a description of an REC sequence overlapping a data transfer). In fact, we don’t even require an REC to have been processed in order to accept an SRR.

Paul Entzel

Quantum

From: owner-t10@t10.org [mailto:owner-t10@t10.org] On Behalf Of Banther, Michael
Sent: Thursday, August 31, 2006 3:43 AM
To: David Peterson
Cc: t10@t10.org
Subject: RE: FCP-4:

Hi Dave,

HP tape drives do not support retrying a sequence of writes from Relative Offset=0. We expect the Relative Offset to match what we reported in a preceding REC. In the REC we report the Relative Offset of the previous XFER_RDY.

Regards,

Michael Banther

Hewlett-Packard Ltd.

+44 117 312 9503

From: David Peterson
Sent: Friday, August 25, 2006 1:38 PM
To: 'BANTHER,MICHAEL (HP-UnitedKingdom,ex2)'; 'Erich Oetting'; 'Greg Wheeless'; 'kdbutt@us.ibm.com'; 'paul.entzel@quantum.com'; 'paul.suhler@quantum.com'
Subject: FCP-4:

Howdy,

I took an action item to contact the tape vendors regarding the Relative Offset value on a retry. From the minutes:

6.1 Relative Offset on retry Peterson/McDATA

In the event of Sequence retry, is the initiator allowed to restart from Relative Offset=0, which forces the target to hold the application client buffer until confirmed completion (may be megabytes)?

Tape vendors say this is ok for reads, but a problem for writes. They are able to back up only to the last XFER_RDY point. This seems to work with all HBAs in use. It is requested to remove the allowance to go back to zero.

ACTION: HBA vendors to determine whether they need to be able to do Sequence retry from relative offset 0.

060711-1 Dave Peterson to contact tape vendors to see whether they are able to force the Sequence Count to zero on Sequence retries.

So what say ye? Note this "feature" has been in place since FCP-2.

The text in question:

12.4.1.7 FCP_DATA IU recovery - read operations

The initiator FCP_Port shall set the RELATIVE OFFSET field in the SRR to that of the next data requested. If the initiator FCP_Port is unable to determine the Relative Offset of the next data requested, the initiator FCP_Port shall set the RELATIVE OFFSET field to zero.

...Dave

(no disclaimer)