03-26-2006
Most tape device drivers in UNIX support compression at the hardware level assuming the physical tape drive supports it. Compression is enabled or disabled by specifying the appropriate tape device. Tape density can also be specified in this manner. Refer to the st(7D) man pages for a detailed list of driver options.
For example:
tar cvf /dev/rmt/0hc directory-name # high density, hardware compression
or
tar cvf /dev/rmt/0h directory-name # high-density, no compression
Remember, hardware compression rarely increases overall capacity if the data stream is already compressed. That is, if all the files in the above example "directory-name" are already compressed, enabling hardware compression won't "double compress" and could easily increase the tape required due to duplicate overhead of the software and hardware compression algorithms.
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LEARN ABOUT DEBIAN
amtapetype
AMTAPETYPE(8) System Administration Commands AMTAPETYPE(8)
NAME
amtapetype - generate a tapetype definition by testing the device directly
SYNOPSIS
amtapetype [-h] [-c] [-f] [-p] [-b blocksize] [-t typename] [-l label] [-o configoption...] [config] [device]
DESCRIPTION
amtapetype generates a tapetype entry for Amanda by testing the device directly.
OPTIONS
Note
The options for amtapetype have changed in version 2.6.1
-h
Display the help message.
-c
Run only the hardware compression detection heuristic test and stop. This takes a few minutes only.
-f
Run amtapetype even if the loaded volume is already labeled.
-p
Run only the device property discovery.
-b blocksize
block size to use with the device (default: 32k)
-t typename
Name to give to the new tapetype definition.
-l label
Label to write on the tape (default is randomly generated).
-o configoption
See the "CONFIGURATION OVERRIDE" section in amanda(8).
If a configuration is specified, it is loaded and used to configure the device. Note that global configuration parameters are not applied
to the device, so if you need to apply properties to a device to run amtapetype, you should supply those properties in a named device
section.
EXAMPLE
Generate a tapetype definition for your tape device:
% amtapetype -f /dev/nst0
NOTES
If the device cannot reliably report its comprssion status (and as of this writing, no devices can do so), hardware compression is detected
by measuring the writing speed difference of the tape drive when writing an amount of compressable and uncompresseable data. If your tape
drive has very large buffers or is very fast, the program could fail to detect hardware compression status reliably.
Volume capacity is determined by writing one large file until an error, interpereted as end-of-tape, is encountered. In the next phase,
about 100 files are written to fill the tape. This second phase will write less data, because each filemark consumes some tape. With a
little arithmetic, amtapetype calculates the size of these filemarks.
All sorts of things might happen to cause the amount of data written to vary enough to generate a strange file mark size guess. A little
more "shoe shining" because of the additional file marks (and flushes), dirt left on the heads from the first pass of a brand new tape, the
temperature/humidity changed during the multi-hour run, a different amount of data was written after the last file mark before EOT was
reported, etc.
Note that the file mark size might really be zero for whatever device this is, and it was just the measured capacity variation that caused
amtapetype to think those extra file marks in pass 2 actually took up space.
SEE ALSO
amanda(8), amanda.conf(5)
The Amanda Wiki: : http://wiki.zmanda.com/
AUTHORS
Dustin J. Mitchell <dustin@zmanda.com>
Zmanda, Inc. (http://www.zmanda.com)
Jean-Louis Martineau <martineau@zmanda.com>
Zmanda, Inc. (http://www.zmanda.com)
Amanda 3.3.1 02/21/2012 AMTAPETYPE(8)