StorageWorks SDLT Tape Drive by Compaq Reference Guide
2–5
Operating System Device Drivers
Compaq Tru64 UNIX
The Compaq Tru64 UNIX operating system uses Dynamic Device Recognition
(DDR) which allows the operating system to recognize the SDLT drive.
If the Tru64 UNIX system does not have a DDR entry to identify the SDLT drive, the
system defaults to a generic SCSI device and to the default settings of the tape drive.
DDR Recognition
NOTE:
Starting with UNIX 5.1, the DDR tables will be changed. The syntax for tape related
commands will also change. The examples included below show the new syntax.
The SDLT drive provides compression so that the storage capability for tapes can be
effectively doubled when the tape drive has been instructed to turn on compression.
This is known as hardware compression. Hardware compression is controlled by the
drive firmware and should be used instead of the software compression that is
sometimes provided by software products. Check the software application manual to
understand the interaction of the application with regard to hardware compression.
The drive is instructed by the user to turn on hardware compression through use of
switches in utilities such as tar. (Additional information is available online. See the
man pages for tz, file, tar, dump and cpio. Additionally the man page for ddr.dbase can
be useful. It is the derivation for the integers associated with compression below).
Turning Compression On
The following sections give 2 examples of turning on compression using the tar
command.
Example 1
An example to turn on compression using a tar command is:
$tar cvf /dev/tape/tape5_d? filename.txt
Where:
•
tape5 = the tape device as known by the system (shown in the file command, in
this case, tape unit 5).
•
? = 0, 2, 4 or 6 will turn hardware compression off (see the SDLT drive description
in the ddr.dbase file online).
•
? = 1, 3, 5 or 7 will turn hardware compression on.