tape compression

[Lonni J Friedman]

On Fri, Feb 29, 2008 at 7:10 AM, C M Reinehr <cmr at amsent.com> wrote:
> On Friday 29 February 2008 06:41, vu pham wrote:
>  > C M Reinehr wrote:
>  > [...]
>  >
>  > >> Do I have to run any extra command to force the tape drive to use
>  > >> compression mode ? I already tried "mt -f /dev/st0 compression 1" but it
>  > >> does not help.
>  > >
>  > > What Bill says is very true, but here are some utilities that can be very
>  > > helpful in figuring out what's going on. The tapeinfo command which comes
>  > > in the mtx package can tell you explicitly if your hardware data
>  > > compression is turned on or off. Check out, also, the scsitape command
>  > > from the same package. Finally, there is the sg3_utils package which
>  > > contains a number of useful SCSI utilities.
>  > >
>  > > Here's what the output of the tapeinfo command looks like on my system
>  > > with a Tandberg LTO2 tapedrive:
>  >
>  > [...]
>  >
>  > > By the way, the command that I use to turn compression on & off is:
>  > > mt -f /dev/nst0 defcompression 1
>  > >
>  > > Another thing is that with some tape drives (or so I've read) is that the
>  > > compression & defcompression commands do not work. You have to set the
>  > > density code.
>  >
>  > CM, thanks for your advice.
>  > I just installed the package mtx, but it complains that there is no sg
>  > devices on my server. This server is a RH9. Can I make it see the tape
>  > drive as sg device ?
>  >
>  > Thanks,
>  >
>  > Vu
>
>  I'm not familiar with RH9 (I switched to Debian some years ago). The /dev/sg*
>  entries are created automagically for me by udev now. But, I would imagine,
>  if RH9 doesn't use udev, that it simply is a matter of using /dev/MAKEDEV to
>  create them.

Sure, but creating them won't do any good if the kernel isn't going to
use them.  You can create a /dev/fubar but its not going to fix
anything.


-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
L. Friedman                                    netllama at gmail.com
LlamaLand                       https://netllama.linux-sxs.org