Unit Attention and Reservation Conflict

Bob Snively Bob.Snively at Eng.Sun.COM
Tue Oct 24 08:58:51 PDT 1995

The basic flaw in this protocol is that you should probably not be
doing this during the bring-up or installation.

SCSI-2 notes that INQUIRY and REQUEST SENSE go through a reservation
without any conflict.  INQUIRY has the additional property of being
able to indicate the presence and type of peripheral even if it
is not ready and even if the LUN is not installed in the target.

Using this information, the best way to bring up a drive is to do:

		Check Condition
		Unit Attention
		defines device type and presence

Then finally do a TEST UNIT READY.

This was explained in the now-defunct annex K of SCSI-2.


>From sgaskill at QNTM.COM Thu Oct  5 11:22:55 1995
>Date: Thu, 5 Oct 1995 10:58:13 -0700
>Subject: Unit Attention and Reservation Conflict
>To: scsi at symbios.com
>Based on section 7.9 in SCSI-2 rev 10K (second half of section) it is unclear as
>to what action the target should take in the following situation.
>1. Target has a pending Unit Attention condition for all initiators.
>2. Initiator A selects the target, gets the Unit Attn, and then creates a 
>"normal" reservation (not 3rd party, not "persistent").
>3. Initiator B issues a Test Unit Ready to the target and gets the Reservation 
>Conflict (higher priority status as noted in 7.9).
>4. Initiator A releases the reservation.
>5. Initiator B issues another Test Unit Ready to the target.
>Q: Will Initiator B get a Unit Attention OR should the UA condition have been 
>cleared by the TUR which resulted in a reservation conflict?
>Alternate question:  What do most peripherals do in this situation?
>Thanks very much for the help.
>  Steve Gaskill
>  Quantum Corp

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