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

[Conor Daly]

Hi,

Still no attachment.  Maybe could you email it direct?

Thanks,

Conor

On Wed, Jun 23, 2010 at 12:03:27AM -0400 or so it is rumoured hereabouts, 
Little Girl thought:
> 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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-- 
Conor Daly <conor.daly at cod.homelinux.org>
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