You are not dreaming.  There is indeed a consistent command syntax, it is
called the SCSI-2 or -3 command set.  It fully details the various commands
available inside libraries.  In simplistic terms, each element within a
library is referenced by an element address and the SCSI command set allows
for actions to be performed on one or more element.   Further some libraries
support extended functions such as door locking, media rotation, etc.

Each library has its own element addressing scheme and either keeps track of
the contents of the elements or can quickly find out the contents on demand.

For instance, let's take an 4-drive, 48-slot HP library, with one robot arm
and 1 mail slot.  The library may address these elements as follows:

Element 0 will be the robot arm.  Element 1, 2, 3 and 4 will be the drives.
Element 10 will be the mail slot and element 31 will be the first tape slot,
along with the next 47 elements.  The last element will be 78, which
corresponds to slot number 48.  The robot control module must be aware of
the element-addressing scheme for the particular library it is controlling,
of course.

Now say I want to load the tape contained in slot 10 into drive 3.  I would
then format and issue a move element command asking for the contents of
element 40 to be moved into element 3.  This is a simple SCSI command
following a very specific format.  (In another library, say a StorageTek
library, the exact same request (load tape 10 into drive 3) could translate
into moving element 264 to element 32, but using the exact same command
format.)  The program then waits for the return information from the
library.  This information follows very specific guidelines and once decoded
can translate into specific messages, such as Source Element empty, target
element full or success.

Beyond the elements (slots) there is a further method to track the tapes
within the library and that is with barcodes.  This is a more flexible
method of control and I highly recommend it.  The move element commands
would then break down into first finding out where the specific barcode is
in the library and then moving that element to the other element.  So, your
external command looks like this:  load tape with barcode DGL711 into drive
3.

I apologize for the length of this post; I guess I have just been spending
too much time with robotic libraries and the SCSI command set over the last
few years.

Denys

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Monday, June 23, 2003 10:57 PM
To: [log in to unmask]
Cc: [log in to unmask]
Subject: Re: HP Tape Libraries

In a message dated 6/9/03 10:12:52 AM Pacific Daylight Time,
[log in to unmask] writes:




Makers of robotic libraries with DLT media include this (non-exhaustive)
list....



Is there such a thing as a consistent command syntax for libraries?  Am I
dreaming?

Wayne

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