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 :)
