amtapetype - generate a tapetype definition.
amtapetype [-h] [-c] [-o] [-b blocksize] [-e estsize] [-f tapedev]
amtapetype generates a tapetype entry for AMANDA.
-h Display an help message.
-c Run only the hardware compression detection heuristic test and
stop. This takes a few minutes only.
-o Overwrite the tape, even if it’s an AMANDA tape.
record block size (default: 32k)
estimated tape size (default: 1g == 1024m)
tape device name (default: $TAPE) The device to perform the
tapetype name (default: unknown-tapetype)
Generate a tapetype definition for your tape device:
% amtapetype -f /dev/nst0
Hardware compression is detected by measuring the writing speed differ-
ence of the tape drive when writing an amount of compressable and un-
compresseable data. It does not rely on the status bits of the tape
drive or the OS parameters. If your tape drive has very large buffers
or is very fast, the program could fail to detect hardware compression
During the first pass, it writes files that are estimated to be 1% of
the expected tape capacity. It gets the expected capacity from the -e
command line flag, or defaults to 1 GByte. In a perfect world (which
means there is zero chance of this happening with tapes :-), there
would be 100 files and 100 file marks.
During the second pass, the file size is cut in half. In that same
fairyland world, this means 200 files and 200 file marks.
In both passes the total amount of data written is summed as well as
the number of file marks written. At the end of the second pass, quot-
ing from the code:
* Compute the size of a filemark as the difference in data written be-
tween pass 1 and pass 2 divided by the difference in number of file
marks written between pass 1 and pass 2. ... *
So if we wrote 1.0 GBytes on the first pass and 100 file marks, and 0.9
GBytes on the second pass with 200 file marks, those additional 100
file marks in the second pass took 0.1 GBytes and therefor a file mark
is 0.001 GBytes (1 MByte).
Note that if the estimated capacity is wrong, the only thing that hap-
pens is a lot more (or less, but unlikely) files, and thus, file marks,
get written. But the math still works out the same. The -e flag is
there to keep the number of file marks down because they can be slow
(since they force the drive to flush all its buffers to physical me-
All sorts of things might happen to cause the amount of data written to
vary enough to generate a big 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 re-
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
It also explains why amtapetype used to sometimes report a negative
file mark size if the math happened to end up that way. When that hap-
pens now we just report it as zero.
Man(1) output converted with