Save Data Pointer questions

Koller, James F TR JFK1 at
Thu Mar 6 13:26:00 PST 1997

* From the SCSI Reflector (scsi at, posted by:
* "Koller, James F             TR" <JFK1 at>

I am working on a multi-processing platform that interfaces to a mainframe 
host as a SCSI target device.  I use the Save Data Pointer - Disconnect 
message-in sequence to allow target disconnects on Read commands.  When it 
occurs, the disconnect sequence immediately follows the command phase in 
which the Read is issued.  The target follows with a reselection to complete 
the command when data is available.  There is never more than one of these 
disconnect-reselect pairs per Read command.

My questions involve the need for a Save Data Pointer message.  Our 
proprietary SCSI host adapter apparently does not require it in the manner 
that I do disconnects.  A commodity host adapter I have recently interfaced 
to also does not require it.  In the latter case, however, the Save Data 
Pointer actually has an occasional adverse effect and is therefore 

Does the industry standard not require a Save Data Pointer message in the 
way that I use it (i.e. sent once before any data is transferred) ?

How can I be sure that, if I omit the Save Data Pointer message, no other 
commodity host adapters I try will have problems?

Jim Koller
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