SAM-3 proposal: ... Data-In and Sense Data sizes
Elliott, Robert (Server Storage)
Elliott at hp.com
Thu Oct 31 06:57:27 PST 2002
* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> -----Original Message-----
> From: Ralph Weber [mailto:ralphoweber at compuserve.com]
> Sent: Wednesday, October 30, 2002 9:31 PM
> To: t10 at t10.org
> Subject: Re: SAM-3 proposal: ... Data-In and Sense Data sizes
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Ralph Weber <ralphoweber at compuserve.com>
> The exposition below appears to be confusing implementation
> with architecture.
> Adding a SENSE LENGTH parameter recommends (or maybe
> requires) that SCSI Transport Protocols include equivalent
> information in their Response IUs.
They all do so to date.
> This may, in due course,
> affect how HBAs are designed but from a SAM perspective that
> is nowhere near as interesting as the requirements placed on
> targets as a result of the necessary requirements in the SCSI
> Transport Protocols.
> As for SENSE LENGTH options, the most straight forward option
> appears to have been overlooked. SPC-3 should be modified to
> require that when allocation length is greater than 8, at
> least 8 bytes of Sense Data shall be returned.
There's no allocation length communicated to the target
For REQUEST SENSE, there is this rule:
"If the allocation length is eighteen or greater, and a device
server returns less than eighteen bytes of data, the application
client should assume that the bytes not transferred would have
been zeros had the evice server returned those bytes."
> The problems with the DATA-IN LENGTH proposition are similar
> to those with SENSE LENGTH. In this case, however, I take the
> absence of suitable information in the SAS Response IU as an
> indication that the current thinking in the industry that
> provision of a DATA-IN LENGTH parameter is inappropriate.
A residual is not provided in SAS response IUs for the same
reason as parallel SCSI - the initiator is lockstepped with
the target and its count of data received should match the
target's count of data transmitted. We're not worried about
losing entire data frames in a vast store-and-forward fabric.
Rob Elliott, elliott at hp.com
Industry Standard Server Storage Advanced Technology
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at t10.org
More information about the T10