[Gllug] How much space left on a tape...

[Russell Howe]

On Wed, Dec 06, 2006 at 12:05:37AM +0000, Adrian McMenamin wrote:
> On Tue, 2006-12-05 at 23:19 +0100, salsaman wrote:
> > Adrian McMenamin wrote:
> > 
> > >Sorry, my original message was unclear. What I mean is I am doing weekly
> > >or so backups on 4GB tapes - the DAT drive capacity is 4GB. How do I
> > >know how close I am to this routine needing to be changed?
> 
> Thanks for the various suggestions. The answer seems to be - if I want
> to do this simply (these are unattended backups that tend to run while I
> am out of the house) there is no simple way - ie I cannot run a simple
> command and have that emailed to me so when I get home I know the backup
> might fail tomorrow/next time with the addition of another 1000 lkml
> messages in the mix.
> 
> I suppose I knew that all along, but just wanted to check

I'm going to assume you're using hardware compression on the drive, so
that the data you send to the drive is being compressed by the drive
itself.

What you really need to know is the compressed size of that data on the
physical tape, and I know of no way to get this information.

dd'ing /dev/zero to the tape would likely be running for quite a while
if the hardware compression isn't completely naiive!

If you're not using hardware compression, then it's quite easy to log
the amount of data written to the tape so far and then discover
empirically how much you can write before your tapes get full (or use a
public database of such information which someone pointed out)

If all you need is the latter, then something like amanda, bacula or
even arkeia can keep a log of tapes and data written to them.

-- 
Russell Howe       | Why be just another cog in the machine,
rhowe at siksai.co.uk | when you can be the spanner in the works?
-------------- next part --------------
-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug