tape: update user docu

docs/tape-backup.rst

@@ -30,3 +30,61 @@ In general, LTO tapes offer the following advantages:
 - Cold Media
 - Movable (storable inside vault)
 - Multiple vendors (for both media and drives)
+
+
+Supported Hardware
+------------------
+
+Proxmox Backup Server supports `Linear Tape Open`_ genertion 3
+(LTO3) or later. In general, all SCSI2 tape drives supported by
+the Linux kernel should work.
+
+Tape changer support is done using the Linux 'mtx' command line
+tool. So any changer devive supported by that tool work work.
+
+
+
+Terminology
+-----------
+
+:Tape Labels: are used to uniquely indentify a tape. You normally use
+   some sticky paper labels and apply them on the front of the
+   cartridge. We additionally store the label text magnetically on the
+   tape (first file on tape).
+
+.. _Code 39: https://en.wikipedia.org/wiki/Code_39
+
+.. _LTO Ultrium Cartridge Label Specification: https://www.ibm.com/support/pages/ibm-lto-ultrium-cartridge-label-specification
+
+:Barcodes: are a special form of tape labels, which are electronically
+   readable. Most LTO tape robots use an 8 character string encoded as
+   `Code 39`_, as definded in the `LTO Ultrium Cartridge Label
+   Specification`_.
+
+   You can either bye such barcode labels from your cartidge vendor,
+   or print them yourself.
+
+.. Note:: Physical labels and the associated adhesive shall have an
+   environmental performance to match or exceed the environmental
+   specifications of the cartridge to which it is applied.
+
+:Media Pools: A media pool is a logical container for tapes. A backup
+   job targets one media pool, so a job only uses tapes from that
+   pool. The pool aditionally defines how long we can append data to a
+   tape (allocation policy), and how long we want to keep that data
+   (retention policy).
+
+:Tape drive: The decive used to read and write data to the tape. There
+   are standalone drives, but drives often ship within tape libraries.
+
+:Tape changer: A device which can change the tapes inside a tape drive
+   (tape robot). They are usually part of a tape library.
+
+.. _Tape Library: https://en.wikipedia.org/wiki/Tape_library
+
+:`Tape library`_: A storage device that contains one or more tape drives,
+   a number of slots to hold tape cartridges, a barcode reader to
+   identify tape cartridges and an automated method for loading tapes
+   (a robot).
+
+   People als call this 'autoloader', 'tape robot' or 'tape jukebox'.