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

Little Girl littlergirl at gmail.com
Wed Jun 23 04:03:27 UTC 2010

Hey there,

Conor Daly wrote:
> On Tue, Jun 22, 2010 at 08:03:22AM -0400 or thereabouts, Little
> Girl wrote:
> > 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 zipped it this time to mailman-proof it. (:
> > 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.

Your examples showed you using what appeared to be normal commands
after the -f part, so I'm hoping you can use the script after the -f
part as well.
> 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
> tape.

My guess is that the compression wouldn't have any effect whatsoever
on the script.

> 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.

The script will check for a specific size in KB, so if you know how
big complete and partial backups are, you could get it to check for
exactly those sizes, and proceed/fail/notify you/etc. based on what
it finds. I hope it will work for you. (:

Little Girl

There is no spoon.

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