Questions on Persistent Reserve

Charles Monia 237-6757 monia at
Mon Jul 1 12:28:30 PDT 1996

* From the SCSI Reflector, posted by:
* Charles Monia 237-6757 <monia at>

I have the following questions on Persistent Reserve (as described in


a) On what basis is a reservation type deemed nonconflicting? The first
paragraph on pp 14 says persistent reservations may be generated "as
long as the reservations are not contrary to existing reservations". The
meaning of "not contrary" is not self-evident.  For instance, does
exclusive read, shared write conflict with shared read, shared write? 
Maybe it would be clearer if the nonconflicting types were enumerated in
a seperate table.

b) What are the interactions with initiators that have no reservations
in effect?  For example, does a read shared, write shared reservation
prohibit a non-reserving initiator from accessing the device?

c) Why is a code 4 reservation ( read shared, write shared) designated
as "non-conflicting, this initiator"?  Why should another initiator be
prohibited from making the same type of reservation?

Reservation Behavior

In FCP and parallel SCSI, reservations are checked using the link
address (FCP port address or SPI bus address). If the address changes, 
the old reservation remains in force and it's the initiator's job to
clean up.  In that case, I assume that a preempt or preempt and clear
using the same key value for the port and preempted port will have the
desired effect of remapping the key to the new link address.  Is that


* Charles Monia Storage Architecture Group                         *
* Digital Equipment, Shrewsbury MA   Internet: monia at   *
* Tel: (508) 841-6757    X400: c=US; a=MCI; o=Digital; ou=SHR      *
* Fax: (508) 841-6100                                              *

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