RE: Data in SCSI Response or SCSI Data

[Robert Snively <rsnively@Brocade.COM>]

In FCP, because FC is a multi-protocol environment that may have
drivers independent of the SCSI drivers, an actual buffer allocation
was transmitted independently of the SCSI command.  Both overrun
and underrun indicators and a residual are returned.  They are 
protocol related, not SCSI related.

There are cases where incorrect length indications are provided 
in the SCSI model for both under-run and over-run cases, but they
are rare and typically associated with legacy tape drive programs.

Bob

>  -----Original Message-----
>  From: Douglas Otis [mailto:dotis@sanlight.net]
>  Sent: Wednesday, September 06, 2000 6:26 PM
>  To: Stephen Bailey; ips@ece.cmu.edu
>  Subject: RE: Data in SCSI Response or SCSI Data
>  
>  
>  Steph,
>  
>  Although a logical use of a residual, I can not see where it 
>  is defined
>  should the allocation length be greater than the returned 
>  length.  Should
>  the allocation be less than the response, this is a Check 
>  Condition and the
>  residual is defined.  It would seem a residual in a case 
>  with adequate
>  allocation is not interesting or defined.  Do you know where 
>  this mechanism
>  you describe is defined?  In normal use, without a Check 
>  Condition such
>  information is not returned to the application.
>  
>  Doug
>  
>  > -----Original Message-----
>  > From: owner-ips@ece.cmu.edu 
>  [mailto:owner-ips@ece.cmu.edu]On Behalf Of
>  > Stephen Bailey
>  > Sent: Wednesday, September 06, 2000 3:45 PM
>  > To: ips@ece.cmu.edu
>  > Subject: Re: Data in SCSI Response or SCSI Data
>  >
>  >
>  > > When do you get GOOD status and residual counts on a read?
>  > What is causing
>  > > the target to get the length wrong?
>  >
>  > One example is an INQUIRY command.  The inquiry data length is
>  > target-specific.  Typically the CDB allocation length (and 
>  DL) are set
>  > to some arbitrary large value (0xff), and the target sends back
>  > everything it has.  The transfer ends with success status.
>  >
>  > There can certainly be transfer residual and no SCSI error status.
>  >
>  > Steph
>  >
>  
>