Residuals On Space Reverse Commands

Jeff_A_Reid at Jeff_A_Reid at
Thu Mar 26 16:14:33 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Jeff_A_Reid at

I had a question about "two's complement residuals".
Part of the discussion in the SCSI-3 group was that how to report
residuals on commands with negative parameters, like Space in
reverse direction, wasn't clear in the ANSI SCSI-2 spec, but in
the spec, in section 8.2.14 Request Sense, about 8 paragraphs after
the sense data format table, after paragraph beginning with
"The contents of the information field...", it states:

"b) the difference (residual) of the requested length minus the
actual length...(Negative values are indicated by two's complement

What wasn't clear about this?

Also the current proposal for Streaming Devices proposes a two's complement
residual, including negative numbers, for illegal length indicator errors
on Read commands, but at the same time proposes using absolute values
(the drive two's complements any negative residual) on Space Reverse

What is the reason for this inconsistency?

Does this mean that a streaming device has to have two different
one for SCSI-2 mode and another for SCSI-3 mode?

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