Paul Suhler Paul.Suhler at Quantum.Com
Wed Mar 18 12:54:18 PDT 2009

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Hi, Geoff.
During the 16 March meeting, the ADI working group discussed the issues
you raised about PREVENT ALLOW MEDIUM REMOVAL.	Item 10.6 of the minutes
	The group concluded that which device has prevent set is not
clear. The library removal can be prevented and the drive media removal
can be prevented. 
	The group concluded that the standard is clear that the library
can always remove the tape regardless of the data transfer device
prevent medium removal setting. 
	After some discussion the group concluded that it would be
useful to define a method for a library to send a command to the DT
device which would clear the prevent setting in the DT device or the
local SMC device server but nobody volunteered to drive a proposal.
Whether the existing PREVENT/ALLOW MEDIUM REMOVAL command could be used
or not was discussed but the consensus was that it probably was not a
good fit.
So, this e-mail is asking for you (or anyone else) to bring in a
proposal addressing the problems.
Thanks very much,
Paul A. Suhler | Firmware Engineer | Quantum Corporation | Office:
949.856.7748 | paul.suhler at 
Disregard the Quantum Corporation confidentiality notice below.  The
information contained in this transmission is not confidential.
Permission is hereby explicitly granted to disclose, copy, and further
distribute to any individuals or organizations, without restriction.
From: GBarton at [mailto:GBarton at] 
Sent: Thursday, March 12, 2009 1:28 PM
To: Paul Suhler
Cc: Williams, Chris (MRO Tape Storage); Curtis Ballard;
Dale.Lafollette at Sun.COM; jon.allen at Sun.COM; kdbutt at;
noud.snelder at; Paul Stone; Rod Wideman; Steven Wallace
Subject: Re: Remaining Work Items for ADI
Thank you Paul for bringing this up. Since I will not be able to attend
T10 this time (who knows when??), I wanted to bring up some issues. 
Regarding handling PREVENT MEDIUM REMOVAL from multiple hosts. 
There some issues that may affect ADI. They are related to PREVENT
MEDIUM REMOVAL specifically and may be related to multiple hosts issuing
the prevent. 
1.  This concerns a PREVENT MEDIUM REMOVAL on a drive (not the library).
We have had requests from customers to be able to override the PREVENT
MEDIUM REMOVAL on a drive to be able to get tapes out in a case such as
losing a host. Also, a tape in a drive may be required to be ejected for
the library to read the barcode or the MAM. I know of no way, other than
cycling power or causing a hard reset on the drive to do this. An ALLOW
through ADI from the library has no affect if the drive follows the
standard (SSC) since the library didn't put the drive in prevent state. 
2.  In the case of the library, a prevent state can be overridden if
needed within the library. However, host connection to the library is
though a drive ADI bridge and if the library overrides the prevent state
and does not restore it, there is no way for the drive to know, and the
drive may not pass through any subsequent PREVENT MEDIUM REMOVAL from
the host. 
3.  For library host connection through a bridged drive, I don't know of
any specific wording that handles multiple hosts issuing PREVENT MEDIUM
REMOVAL through a bridge. Specifically, the drive needs to keep track of
the prevented state since this is initiator dependent. At least some
(perhaps all) of the drives seem to handle this OK but perhaps not
consistent from vendor to vendor. 
Geoffrey L. Barton
Overland Storage
4820 Overland Ave.
San Diego, CA 92123
858 974-4586
gbarton at 

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