How should media information be indexed for SMC commands?

Ballard, Curtis C (StorageWorks) curtis.ballard at
Wed Aug 16 15:17:40 PDT 2006

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I'm working on a proposal for SMC-3 to allow the library to return
information about the media currently in the library.
In SMC-2 everything is based on element numbers and all data requests
are indexed by an element number.
I suspect that applications don't really care about the elements as much
as they care about the volumes in those elements.
When accessing information about media the obvious extension to the
current behavior would be to ask for information about the volume in an
element and index it by element number.  I feel that would work but it
doesn't feel natural.
I've been considering having multiple ways to access information about a
volume and making it possible to ask for information about a volume by a
handle as well as by an element.  If the handle is used one of the
characteristics could be "what element is this volume in."
If accessing volume information by a handle is allowed there are a
couple of possible handles.  The obvious handle is a barcode value but
there is very little control over barcodes and some medium changers
allow duplicate barcodes.  There are also medium changers that don't
have barcode support.
Most media has some form of identifier written to the media now and some
of the media types have world wide unique identifiers so that identifier
would be the most unique but not the most user friendly.
I'm starting to lean towards having a command with a field for volume
identifier and then a second field for volume identifier type.	That way
an application could provide an identifier type of "element number" and
the library would report the information for the volume in that element
but an application could also use a media identifier or barcode.
Curtis Ballard
Hewlett Packard
StorageWorks Tape Automation

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