cartridge tape designators

[andrew yeomans]

I prepared the following fact sheet on both the 9-track tape unit which we
use, and the Sun cartridges.

The info on the 9-track tape drive was obtained from mtio(4), xt(4S) and a
fair bit of experimentation. If you are lucky, it may also be true for
your own mag tape drives.

The info on the cartridge tapes comes from mtio(4), st(S) and several
contributors to Sun-Spots [sorry, I've forgotten who sent what]. The
bottom line is that there is very little to choose between rst0 and rst8
for the amount of data you get on the tape. However, whichever you choose,
you won't be able to read the tape back on some other machines!  Sun-Spots
also explained the problems of booting SunOS installation tapes - If I
remember correctly, the boot proms in the earlier Sun 3 workstations could
only read QIC-11 format. Sun in their wisdom supplied SunOS 4 in QIC-24
format, necessitating users to upgrade their boot proms.

                                                           ___    ___    ___ 
 Andrew Yeomans             PSTN: 0442 230000 ext 3371    |XXX|  |XXX|  |   |
 Crosfield Electronics Ltd  INTL: +44 442 230000          |XXX|  |XXX|  |___|
 Three Cherry Trees Lane    Fax:  0442 232301              ___    ___    ___ 
 Hemel Hempstead            UUCP: ajy at cel.uucp            |XXX|  |   |  |   |
 Hertfordshire              or mcvax!cel!ajy at uunet.uu.net |XXX|  |___|  |___|
 HP2 7RH                                                   ___    ___    ___ 
 England                 .. all opinions are my own, etc. |XXX|  |XXX|  |   |
                         'The network is the bottleneck'  |XXX|  |XXX|  |___|

-------------------------- cut here -------------------------------------
		Magnetic tape devices
		---------------------
xt - Xylogics 472 1/2 inch tape controller
------------------------------------------
Device name		Maj Min	Rewind on close Density	  Block size
Fixed block size mode:
/dev/mt0		 8   0	Rewinding	1600 bpi  2048 bytes
/dev/nmt0  =/dev/mt4	 8   4	Non-rewinding	1600 bpi  2048 bytes
/dev/mt8		 8   8	Rewinding	6250 bpi  2048 bytes
/dev/nmt8  =/dev/mt12	 8  12	Non-rewinding	6250 bpi  2048 bytes

Variable block size (raw) mode:
/dev/rmt0		30   0	Rewinding	1600 bpi  Variable
/dev/nrmt0 =/dev/rmt4	30   4	Non-rewinding	1600 bpi  Variable
/dev/rmt8		30   8	Rewinding	6250 bpi  Variable
/dev/nrmt8 =/dev/rmt12	30  12	Non-rewinding	6250 bpi  Variable

For compatibility reasons, the non-rewinding devices can be accessed by
either of the two names given.

'tar' and 'dump' default to using /dev/rmt8 (rewinding).
'mt' defaults to using /dev/rmt12 (non-rewinding).

The tape density may only be changed when writing if the tape is at the 
load point, and if the drive is set to 'host-selectable density'.

The actual recorded tape density is used when reading or when writing
other than at load point, and any attempts to set it (on the front panel
or by device name) are ignored. The density status lights show the 
selected density, not the actual recorded tape density.

st - SCSI 1/4 inch cartridge tape
---------------------------------
Device name		Maj Min	Rewind on close Format	  Block size
/dev/rst0		18   0	Rewinding	QIC-11	  512*n bytes
/dev/nrst0		18   4	Non-rewinding	QIC-11	  512*n bytes
/dev/rst8		18   8	Rewinding	QIC-24	  512*n bytes
/dev/nrst8		18  12	Non-rewinding	QIC-24	  512*n bytes

There are two parameters to consider with 1/4 inch cartridge tapes.
One is the number of tracks (4 or 9), the other is the encoding format
(QIC-11 or QIC-24). QIC-11 uses 1 byte block numbers, while QIC-24 uses 
3 byte block numbers. QIC-11 has fractionally greater tape density, 
while QIC-24 is more robust.

Tapes written by a 4-track drive can be read on a 9-track drive.
Tapes written by a 9-track drive may sometimes be read on a 4-track 
drive, but with no guarantee of success.

Old   Sun-2 machines can only write 4-track QIC-11 tapes.
Newer Sun-2 machines can only write 9-track QIC-11 tapes.
Sun-3 machines can only write 9-track QIC-11 or 9-track QIC-24 tapes.


					Andrew J. V. Yeomans
					14th June 1989