After degaussing DDS3 tape unusable?!

[Brad Marks]

After having degaussed a DDS3 tape and I fbackup a single file to it, although I'm told:
fbackup(3205): WARNING: unable to read a volume header
fbackup(3024): writing volume 1 to the output file /dev/rmt/0m

when I try to frecover the file, I'm told:
frecover(2105): did not find expected file marker
frecover(5409): unable to read volume header
frecover(5418): not an fbackup volume; unable to read volume header
frecover(2105): did not find expected file marker

Also, the fbackup/frecover takes 654 seconds; with a brand new DDS3 it takes 23 seconds.

Was I misinformed when I heard that it was safe to degauss a DDS tape but not an LTO or DLT (so far, I've been successful with DLT but not DDS -- not quite what I expected!)?
Thanks,
Brad

[Bob E Campbell]

I do not remember DDS tapes being preformatted like the ancient tapes were, but DDS tapes do have a short lifespan for writing (100 full writes). Was the tape known to be good prior to the degauss?

Try running "mediainit -r" against it. Keep in mind that the value of *blank* media is in the realm of $5...

[Bill Hassell · Accepted solution]

It is NEVER recommended to degauss modern tape media such as DDS, LTO, AIT, 9840 etc. ( DLT's are an exception) DDS tapes are not pre-formatted in the way that old cartridge tapes were (servo markers) but they do have a data area at the front of the tape which is only seen (and written) by the drive. It includes insertion counts, writes and reads and other drive-specific data. The other problem is that degaussing can alter the tape's magnetic properties if it is not done very carefully. Even with old reel-to-reel tapes, accidentally turning off the coil will severely damage the media's recording quality (this is true for DLT's too). Still another problem is controlling the proper magnetic strength to truly remove the data patterns. Check this link:

http://www.imation.ca/en_CA/whitepaper/pdfs/WhitePaper_ABCofDegaussing.pdf

For this message:

fbackup(3205): WARNING: unable to read a volume header

is absolutely normal because fbackup is looking for a previous fbackup tape header. Since none was found, fbackup issues the warning in case you were expecting the tape to have been previously written by fbackup in the past. The reason these headers are so important is to prevent overwriting a tape in a multi-tape backup. Once written by fbackup, the warning will disappear in future uses of the tape. This is what commercial backup programs due when they 'initialize' or serialize tapes before usage.

NOTE: For *all* modern tapes, you can instantly remove access to data on the tape by simply writing one small file to the tape. Modern drives will write an end-of-tape marker after the last write and rewind. This marker cannot be bypassed so it renders the rest of the data unreadable. (OK, with very expensive equipment, the marker can be skipped but not with commercial tape drives)

If the data must be truly unreadable, the steps are (in order of increasing paranoia and labor costs):

- write a small file to the tape
- write the entire tape with a data pattern
- write the entire tape 3 times with different patterns
- write the entire 15 times with random data
- smash the tape with a hammer
- run the tape through a media shredder
- incinerate the tape

[Brad Marks]

Thanks all. No more playing with the degausser for me!
-Brad