How do I erase a tape?

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A. The trick is to use a bulk degausser, otherwise known as an industrial strength magnet. Ulrich Oldendorf offered (19 May 2000) these guidelines for selecting a bulk degausser: I found the following by chance at www.dlttape.com: What is the industry standard for degaussing DLT tapes? Media is rated in coercivity, as stated below. Compact III is rated at around 1540 Oersteds (1600 Oe). Compact IV is rated at around 1850 Oersteds (2000 Oe).

The rule of thumb with degausses is 2 to 3 times the coercivity of the media. For instance,in our startup manufacturing area we use a degausser that has a rating of around 4000 Oersteds. Tape goes into the degausser 1 pass and then turn it 90 degrees and pass it through again. The manufacturers of degaussers don't specify the exact Oersteds rating of their machines. Rather, they say if you have media with a specific Oersteds rating, then use a specific machine.

Erasure depth is measured in DB's, but if you use the rule of thumb above, and use what a manufacturer recommends, you should be safe. Depth of erasure may be called out in the manufacturers spec but they have already figured out which machine to use for you.

We do not have a standard degausser that we use. However, the ones we use are:

• Weircliffe Bulk Eraser Model No. BTE 1910L
• Weircliffe Internationa lLTD. Exeter, England http://www.weircliffe.co.uk/
• Garner Eliminator 4000 Model No. 4000
• Garner Industries Lincoln Nebraska http://www.garnerindustries.com/

If you just want to scramble the contents of the tape so that it looks like a fresh and unused tape to networker, there's an "erase" command bundled with NetWorker. It can be found in /etc/LGTOuscsi on most *nix'es and in the nsr\bin directory on NT/Win2000. The command takes a few arguments, most important is the SCSI target you want to point it at. To just erase the label instead of the whole tape (much faster) you can spesify the -s switch. The -r switch will rewind the tape before it's erased. Here's a sample command;

   erase -rs -a 1.1.0

The numbers point to SCSI bus number 1, SCSI ID 1 and LUN 0. If you want to bulk erase a lot of tapes in a jukebox with this command, you would need to create a script that mounts tapes (you can use "nsrjb" for this), runs erase, then unmounts tapes.. If there's no tape at the spesified target, erase will fail.

"erase" is a system command on some systems (NT) so you might have to run the erase command with full path or with .\ as a prefix if you're already in the right directory.