[rescue] mt erase

Michael Parson mparson at bl.org
Thu May 10 18:53:37 CDT 2007

On Thu, May 10, 2007 at 06:31:11PM -0400, brian wheeler wrote:
> On Thu, 2007-05-10 at 16:59 -0500, Doug McLaren wrote:
>> On Thu, May 10, 2007 at 01:31:15PM -0400, Lord Doomicus wrote:
>> | I've erased tapes using  dd if=/dev/random of=/dev/mt0 bs=<block size  
>> | of tape>count=<number of blocks on tape>
>> | 
>> | if you don't have /dev/random ( not on a lot of older platforms ),  
>> | you should be able to use /dev/zero.
>> Depending on your OS, you might prefer /dev/urandom.  At least under
>> Linux, /dev/random blocks when it runs out of entropy, and so to come
>> up with many gigabytes to erase a tape would take ages.  A quick test
>> on my computer showed /dev/random emitting data at about 16 bytes/s --
>> so that 5 GB tape will take about 10 years to erase.  Perhaps you can
>> speed this up signifigantly, but ...
>> /dev/urandom will reuse it's entropy once it runs out, so it's go MUCH
>> faster.  (And the data will probably be more than random enough.)
>> Using /dev/zero, especially just once, will certainly make reading the
>> tape much harder, but I wouldn't rely on it to protect sensitive data
>> from anybody who has physical access to the tape.
>> (I'm not really looking to get into secure deletion here ...)
>> Do be careful if you decide to use a degausser -- you need a really
>> strong one for modern tapes.  For example, a cheap degausser found at
>> Radio Shack for cassette tapes will have zero effect on a DLT tape, no
>> matter how long it's applied -- the tape will still be readable
>> without even any errors.
> Not to mention that if you do use a strong degausser you may ruin some
> types of media that have a servo track on them (IBM 3590?  Others?)

Can't reuse LTO after being degaussed.

Michael Parson
mparson at bl.org

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