Here's some more info on tape drives.
Alan Rollow - Dr. File System's Home for Wayward Inodes.
alan_at_nabeth.cxo.dec.com
re: tape densities.
All tapes are different. Once upon a time the most common
tape in use were 7 track tapes that probably supported a
single density. Then 9 track tapes came along and supported
800 bpi, 1600 bpi and 6250 bpi. Most drives supported two
of the three, though there were some that supported all three.
With the advent of compression, the tendency is to use the
high density device as the one to enable compression and the
low density device as no compression. For drives with a
single density offering, such as the RDAT family, this
is easy.
So this means, that for TZ07 drive there is only one physical density.
In you want not to turn on software compression, use /dev/nrmt0l. If you
wan to turn on hardware compression, use /dev/nrmt0h. That also implicates
that probably don't need to even check the DIP switch on the drive!
Other drives offer more choices. The DLT family from Quantum
(originally from us) has supported a host of densities. The
DLT2000 (TZ87) can write three uncompressed formats and one
of those supports compression. That's four effective densities.
The DLT7000 (TZ89) supports eight, but only four per tape
cartridge type. Digital UNIX can get to six of those as
distributed.
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Received on Sun Nov 30 1997 - 12:41:22 NZDT