Unit Attention and Reservation Conflict

ljr at austin.ibm.com ljr at austin.ibm.com
Wed Oct 25 05:46:55 PDT 1995

Bob Snively writes:
>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:
>        INQUIRY
>                Check Condition
>                Unit Attention
>        INQUIRY
>                defines device type and presence
>Then finally do a TEST UNIT READY.

However, most drives will not return CHECK CONDITION on an INQUIRY command.  
SCSI-2 10L section 8.2.5 explicitly says that "The INQUIRY command shall return 
CHECK CONDITION status only when the target cannot return the requested INQUIRY 
data."  Many drives I have experience with will return INQUIRY data in response
to the INQUIRY command even while spun down.

Les Record
ljr at austin.ibm.com
(512) 838-3622
Austin, Texas

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