Read Element Status and Reservation Conflicts

robbyb at robbyb at
Mon May 19 10:29:29 PDT 1997

* From the SCSI Reflector (scsi at, posted by:
* robbyb at vnet.IBM.COM
Subject: Read Element Status and Reservation Conflicts
At the SMC working group in Natick some concerns were brought
up relative to X3T10/96-267-r2.  In an attempt to get this
through with fewer problems I am posting what I plan to do
for revision 3.  (I posted a revision 2 proposal and didn't
get any responses until the Natick meeting).  Please contact me
before the working meeting on this if you have any concerns
because we want to get the SMC document out very soon.

The text for revision 3 follows:

At the present time, the ability to acquire information through a
Reservation is limited.  However, a situation has arisen that seems
to require opening up the window a bit.  The READ ELEMENT STATUS
response data is used in a way similar to INQUIRY data.  It is
needed to correctly initialize the library management software
for some initiators.

In particular, with an attached Medium Changer or any independent
Medium Changer, a READ ELEMENT STATUS command is blocked from
responding wtih other than RESERVATION CONFLICT status.  Also,
a NOT READY condition can cause problems at initialization time.

We propose that a bit 0 byte 10, CURDATA, be defined for the
READ ELEMENT STATUS command.  If the bit is 1 it requires
the drive to return all currently known data, even
if a RESERVATION CONFLICT or NOT READY condition exists.  This
proposal in no way affects the format of the data or the manner of
specifiying which data to return but rather modifies the
circumstances under which READ ELEMENT STATUS data is returned.
When the CURDATA is 1, the device shall not do any motion
for the command but rather return data that is currently available
When CURDATA is 0, the READ ELEMENT STATUS command behavior is
the same as presently defined.

             Rob Basham

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