* Paul Bijnens <paul.bijnens AT xplanation DOT com> [20030619 16:43]:
> Joshua Baker-LePain wrote:
> 
> >On Thu, 19 Jun 2003 at 4:57pm, Tom Brown wrote
> >
> >  
> >
> >>>ISTR you saying this is Linux?  If so, then 'mt compression 0' should do
> >>>it.  You can check the status by pointing 'tapeinfo' (from the mtx
> >>>distribution) at the generic device associated with your tape drive.
> >>>      
> >>>
> >>It is linux yes - will amanda use this command before writing to this device
> >>when amanda runs normally? How can one be sure that the hardware compression
> >>is permanently off?
> >>    
> >>
> >
> >I just put that command in the script that runs amdump each night.  You 
> >can also play with stinit, but I've never bothered.
> >
> >  
> >
> 
> On Linux this does not help.  Because despite the setting of the "mt"
> command,  the system adapts itself to the setting of the current
> tape if you read from it.  Before writing the new label amanda reads
> the label, thereby reverting to the setting that was used when the tape
> was labeled.
> Even amlabel first reads the tape to check, thereby falling into
> the same trap.
> The only way to switch a tape is: first set the mode "mt ...", and write
> some data on it, *without* any intervening reads.  (Try "mt status"
> afterwards to verify the status of the drive.)
> 
> To configure a drive during boot or on module load),
> configure a file /etc/stinit.def  (see cryptic manpage for "stinit",
> and read README.st in the kernel sources). E.g. for
> a DDS-2 drive (the manufacture and model must be
> exactly as reported by the scsi probes):
> 
> $ cat /etc/stinit.def
> # DDS-2 drive
> manufacturer=ARCHIVE  model = "Python 02635-XXX" {
>   can-bsr can-partitions auto-lock
>   mode1 blocksize = 0 compression = 0
>   #mode2 blocksize = 512 compression = 0
>   #mode3 blocksize = 0 compression = 1
>   #mode4 blocksize = 512 compression = 1
> }
> 

On a Linux-RH I own I have:

malin@malinmalin:~$ cat /etc/stinit.def
# A compressing DAT
manufacturer=ARCHIVE model = "Python 00095-001" {
scsi2logical=1 can-bsr can-partitions auto-lock
mode1 blocksize=0    compression=0 density=0x24
mode2 blocksize=1024 compression=0 density=0x24
mode3 blocksize=0    compression=1 density=0x24
mode4 blocksize=1024 compression=1 density=0x24}

and the stanza "post-install st /sbin/stinit" in /etc/modules.conf
so that when the modules load stinit read /etc/stinit.def and do
the Right Thing.

Now what I don't remember is how the tape devices in /dev
are related to the entries in stinit.def:

malin@malinmalin:~$ ls -l /dev/nst0*
crw-rw----    1 root     disk       9, 128 Apr 11  2002 /dev/nst0
crw-rw----    1 root     disk       9, 224 Apr 11  2002 /dev/nst0a
crw-rw----    1 root     disk       9, 160 Apr 11  2002 /dev/nst0l
crw-rw----    1 root     disk       9, 192 Apr 11  2002 /dev/nst0m

How to decide which device is variable/fixed block size and
with or without compression? I've done this such a long time 
ago!

jf
-- 
don't chatter in hopes of favor or gain.
when touched now by pleasure, now by pain.