[Converted to WordStar format by J. Lohmeyer 10/19/87]




To:    John Lohmeyer, Chairman X3T9.2

From:  Dan Davies

Subj:  Sequential Access Buffered Mode Two


Buffered Mode Two is intended for multiple-initiator systems that require 
independent recovery paths for write error processing.  Buffered mode one 
allows the target to buffer any number of blocks from any number of 
initiators.  The first initiator to discover a deferred write error is 
responsible for the entire error recovery procedure, regardless of that 
initiator's affiliation with the unwritten data.  With buffered mode two, the 
target is allowed to buffer any number of blocks from any single initiator.  
If a new initiator issues a write command while write data remains in the 
buffer for a different initiator, the target will synchronize the buffer 
before accepting any data from the new initiator.  This prevents any mixing of 
data in the buffer and allows the target to preserve any buffered data for the 
"owning" initiator.


1) Buffered Mode Two MODE SELECT/MODE SENSE wording.

Add the following wording to the MODE SELECT command on page 9-10 and to the 
MODE SENSE command on page 9-28:

"  2h The target may report GOOD status on a WRITE command as soon as the data 
   block has been successfully transferred to the target's buffer.  One or 
   more blocks may be buffered from any one initiator prior to writing the 
   block(s) to the medium.  If an initiator issues a WRITE command while the 
   buffer contains write data from a different initiator, the target shall 
   write any buffered data to the medium before accepting any data from the 
   new initiator."


2) Deferred Write Error Reporting/Recovery.

Add the following new section to the WRITE command on page 9-48:

"  9.1.17.1  Deferred Write Errors

   A deferred write error condition occurs when the target detects an error 
   has occurred on a buffered write command that previously reported GOOD 
   status.  This condition shall persist until the error is reported and error 
   recovery (if any) is completed. A BUS DEVICE RESET message or a hard reset 
   condition shall also clear the deferred error condition. "
"  If the deferred write error occurs in buffered mode one, the error shall be 
   reported to the first initiator issuing a command (other than INQUIRY or 
   REQUEST SENSE) or the first initiator to respond to Asynchronous Event 
   Notification (if supported).  All other initiators shall receive BUSY 
   status until the deferred error condition is cleared. If the deferred write 
   error occurs in buffered mode two, the error will be reported to the 
   initiator with unwritten data in the buffer.  All other initiators shall 
   receive BUSY status until the deferred error condition is cleared.  
  
   If the error is reported using Asynchronous Event Notification, the target 
   shall send the INITIATE RECOVERY MODE message after successfully 
   transferring the IDENTIFY message for the SEND command.  If this message is 
   successfully transferred, all other initiators shall receive BUSY status 
   until the deferred error condition is cleared by a RELEASE   RECOVERY MODE 
   message from the initiator receiving the INITIATE RECOVERY MODE message.

   If Asynchronous Event Notification is not supported, the target shall send 
   the INITIATE RECOVERY MODE message immediately after successfully 
   transferring the CHECK CONDITION status for the command receiving the 
   deferred error indication.  If this message is successfully transferred, 
   all other initiators shall receive BUSY status until the deferred error 
   condition is cleared by a RELEASE RECOVERY MODE message from the initiator 
   receiving the INITIATE RECOVERY MODE message.

   The deferred error condition shall also be cleared if the initiator rejects 
   the INITIATE RECOVERY MODE message, a BUS DEVICE RESET message is received 
   from any initiator, or a hard reset condition is detected at the target. "