Re: SCSI tape drive and compression

[Philippe Troin <phil@fifi.org>]

Martin Sanborn <marty@delirium.cqe.nwu.edu> writes:

> On Monday 12 November 2001 05:01 pm, Philippe Troin wrote:
> > Martin Sanborn <marty@delirium.cqe.nwu.edu> writes:
> > > How do I turn on the data compression? The mt man page indicates that
> > >
> > > mt -f /dev/tapes/tape0/mtn datcompression [x]
> >
> > mt datcompression 1 (default) reports the current state
> > mt datcompression 0 turns it off
> > mt datcompression 2 turns it on
> 
> Unfortunately, the command mt -f [device] datcompression 2 returns
> 
> Compression off.
> Compression capable.
> Decompression capable.
> 
> I retried dump again just in case it wasn't reporting the compression as on, 
> but still the same behavior (a little less than 4GB on the tape).

Really odd.

> > You might also want to investigate the mt-st package which should give
> > you more control on SCSI tape behavior.
> 
> That one doesn't want to talk to me. I installed it, and I used the command 
> "mt-st -f [device] defcompression". While the tape spins, when it stops it 
> returns nothing. I tried appending a 0,1, or 2 to the end of the command, but 
> it still returns nothing. 
> 
> Again, I tried dump after using the "mt-st defcompression 2"
> command, and the result is still the same. Puzzling.

Have you simply tried "mt-st -f <device> compression 1" ?

What does mt-st prints when you reboot and/or install the st module ?
Mine says:

st0: Mode 0 options: buffer writes: 1, async writes: 1, read ahead: 1
st0:    can bsr: 1, two FMs: 0, fast mteom: 0, auto lock: 1,
st0:    defs for wr: 1, no block limits: 0, partitions: 1, s2 log: 1
st0:    sysv: 0
st0: Default block size set to 0 bytes.
st0: Compression default set to 1

Phil.