[Techtalk] Detect if Dump used multiple tapes for backup.

Conor Daly c.daly at met.ie
Tue Jun 22 12:31:23 UTC 2010

On Tue, Jun 22, 2010 at 08:03:22AM -0400 or thereabouts, Little Girl wrote:
> Hey there,
> Conor Daly wrote:
> > I'm backing up a 300Gb filesystem to an SDLT320 tape and,
> > occasionally, the weekly level 0 dump will overflow to a second
> > tape.
> > 
> I'm not sure if this will be of any use to you, but I've attached a
> small Bash script that checks the size of a directory (in KB) and
> displays the results (also ringing the system bell for undesired
> results). Maybe you could add something like this into the mix.

I think the script got stripped by the mailman software...
> I don't have any magnetic tapes, so I don't know if regular
> scripts will even work on them. If this is totally off base,
> please ignore. (:

Mag tapes are a different kind of storage.  Basically data gets written /
read sequentially so there's no real way to interact with a tape.  Depending
on the software that wrote the tape, there may be a catalogue stored at the
beginning of the tape but there's no real way to know about size stored.

In particular, tape capacity is usually quoted as uncompressed / compressed
size.  So, our SDLT320 tape is a 160Gb uncompressed / 320Gb compressed tape.
In the normal course, the tape drive will do hardware compression of data
and this will do a good job of squeezing data onto the tape unless the data
consists of already compressed files (eg. images, tarballs etc).  Given that
a lot of our data is stored as images, we will occasionally overrun a single

My current problem is that I can't come up with an easy way to check if a
particular tape contains a complete or only partial backup.  At the moment
I'm leaning towards the notion of keeping a tally on the main disk of which
tape has what and using that to decide which tape to write to next.


Conor Daly,                   
Met Eireann, Glasnevin Hill,  
Dublin 9, Ireland             
Ph +3531 8064276 Fax +3531 8064247

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