On FreeBSD, assuming your tape is /dev/sa0
$ mt comp off
will disable compression and
$ mt comp on
will enable compression.
$ mt status
will display the state of the tape drive at the moment. Read man mt for
details.
On Tue, 2002-03-26 at 14:53, Fernan Aguero wrote:
> I'm trying to understand why amanda is only writing approximately
> 19-20 GB on my DDS-4 tapes (HP C5718A, min 20GB and up to 40GB with
> compression).
>
> Supposedly, my DAT40i drive is set from factory with hardware
> compression ON, and host control ON.
>
> According to the documentation that came with the driver, the
> compression is managed through the use of different devices. In the
> same spirit that we have /dev/sa (rewinding) and /dev/nrsa
> (non-rewinding) devices, there is a naming scheme for compression and
> no-compression devices.
> However I don't know which is my device naming convention (FreeBSD
> here).
>
> According to sa(4), on the BUGS section of the man page, I can read:
> "Fine grained density and compression mode support that is bound to
> specific device names needs to be added."
>
> So apparently we're left without it ...
>
> Now how am I supposed to control hw compression? Only through the
> jumpers in the drive? Once and for all?
> I know I can configure amanda to do software compression, this is
> pretty well explained through examples and there are lots of dumptypes
> already there. And I also read that doing both is not recommended.
>
> Problem is: I'd like to use hardware compression and leave my machines
> as light as possible on cpu usage. But how do I know if hardware
> compression is taking place?
>
> i) if the factory default is to have 'host control' ON and I cannot
> do any control from the host over hw compression, should I turn
> 'host control' to OFF?
> If i do this, then upon checking the status of the drive I get a
> column that says 'Compression: unsupported' instead of 'Compression
> DCLZ'
>
> ii) perhaps the compression is taking place but my tapetype
> definition is wrong? The following definition was taken from the
> FAQ-O-Matic, although it didn't mention the type of cartridge used:
>
> define tapetype HP-SURESTORE-DAT40 {
> comment "just produced by tapetype program"
> length 19560 mbytes
> filemark 1147 kbytes
> speed 2957 kps
> lbl-templ "/usr/local/etc/amanda/normal/HP-DAT.ps"
> }
>
> Maybe I should run tapetype myself with my hw compression settings
> and see if I can get over 20GB of data into the tape?
>
> Or perhaps some of you are using the same drive with the same cartridges
> and can share your tapetype def with me?
>
> What happens if I lie to amanda and set the length to 40000mbytes?
> If it reaches the end of the tape, it will reprogram the failed
> filesystems for the next tape, right?
>
> Perhaps this is why now amanda is skipping some large filesystems ...
> Could it be that amanda is not even attempting to write to tape
> because of what the tapetype entry says about the length?
>
> (my largest partition is about 13GB with about 25-40% of it being already
> gzipped files)
>
>
> Thanks in advance,
>
> Fernan
>
> yes, a newbie :)
>
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