Disks and Reservations

Kevin D Butt kdbutt at us.ibm.com
Tue Jun 25 13:30:25 PDT 2013

Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1306251_f.htm">HTML-formatted message</a>

I am struggling to understand Reservations in the disk world.  Me being a 
tape person, my mind set is wrapped around protecting the logical position 
of the tape. This is does not seem to be a concern for disks.
What are the reasons reservations are used in the disk world?  I assume it 
is to protect a Logical Unit for one applications sole use (at least 
writing).  Are there other conceptual reasons?
What are the reasons that a PREEMPT would be used?  In the tape world, 
PREEMPT is typically only used to perform a fail-over from a lost I_T 
nexus to an alternate path.  Is this the same in the disk world, or are 
there other reasons?
Also, sometimes in the tape world, Unit Attentions are ignored.  Is this 
the same in the disk world, specifically related to reservations?
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com

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