GNU bug report logs - #17149
shred - tape data

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From: Rupert Russell <Rupert.Russell <at> ilmor.co.uk>
To: 'Pádraig Brady' <P <at> draigBrady.com>
Cc: "17149 <at> debbugs.gnu.org" <17149 <at> debbugs.gnu.org>
Subject: bug#17149: shred - tape data
Date: Tue, 1 Apr 2014 12:18:22 +0000

Pádraig,

This seems to be getting my task done.

for i in $(seq 1 $NUMTAPES) ; do
		mtx -f $LOADER load $i
	for j in $(seq 1 $NUMWIPES); do 
			shred -v -n 1 $TAPE
 			mt -f $TAPE rewind
	done         
           		shred -v -z -n 0 $TAPE
		mt -f $TAPE rewind
		mtx -f $LOADER unload $i
done

By the way, is there a difference between what these two write to the media?
mt -f $TAPE erase   and
shred -z -n 0 $TAPE

Regards

Rupert Russell
OPERATIONS MANAGER



Ilmor Engineering Ltd
Quarry Road, Brixworth, Northamptonshire, NN6 9UB, UK

Direct:     +44 (0)1604 799105
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-----Original Message-----
From: Pádraig Brady [mailto:P <at> draigBrady.com] 
Sent: 31 March 2014 18:33
To: Rupert Russell
Cc: 17149 <at> debbugs.gnu.org
Subject: Re: bug#17149: shred - tape data

On 03/31/2014 12:00 PM, Rupert Russell wrote:
> Hi,
> 
> shred -v /dev/st0    # where /dev/st0 is the drive in a multi tape carousel.
> 
> This starts well with.
> Pass 1/4 (random) 15MiB
> Pass 1/4 (random) 41MiB
> Pass 1/4 (random) 70MiB
> Pass 1/4 (random).....etc
> 
> But when the end of a 200GiB tape is reached in pass 1, 'shred' doesn't appear to trigger a rewind or maybe wait for the tape to be rewound before attempting to overwrite the data.
> 
> 
> The final messages before and around the error are:-
> 
> Pass 1/4 (random) 190GiB/190GiB  100%
> 
> Pass 2/4 (random)
> 
> Error writing at offset 1288. No space left on device.
> 
> (The next line in my script then runs and unloads the tape.)
> 
> Is this not rewinding the tape a bug or my mis-use of the 'shred' command?

shred(1) doesn't rewind the tape.

It could issue an MTREW ioctl or something, though I suspect there are all sorts of ioctls to consider depending on plaftorm.

I also see the `mt erase` command/ioctl which might suffice?

If not then explicitly handling the tape like this might suffice?

for i in $(seq 3); do
  mt -f /dev/st0 rewind
  shred -n1 /dev/st0
done

thanks,
Pádraig.

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