scrubbing tapes in hp-ux

[VK2COT]

Hello,

HP-UX 11.31 has a DoD 5220.22-M compliant tool to run disk scrubbing. Hp-UX is the only
Unix that I know of to have such a native
OS tool. To check if your version
supports it:

# mediainit | grep scrub

Of course, in some very sensitive environments,
as you said, media has to be destroyed
physically in the end...

Cheers,

VK2COT

[Bill Hassell]

> DDS, DLT, SDLT...no servos

Correct. My blanket statement left off the magnet bias effects which can render virtually all tapes as unusable. In the good old days, the bulk eraser was called a degausser and would run off AC power thus creating constantly changing magnetic polarities. You would turn on the unit, move it close to the media, then slowly pull it away so as not to leave a magnetic bias. This bias decreases the signal to noise ratio which becomes increasingly more critical as the tape density increases. A permanent magnet will definitely cause magnetic bias unless the user constantly twists the magnet to simulate alternating magnetic polarity. This can affect even the ancient 1/2inch reel to reel tapes (first hand experience).

[Steven Schweda]

> My blanket statement left off the magnet
> bias effects which can render virtually all
> tapes as unusable. [...]

This sounds to me like (still) more nonsense.

First, I never said which kind of "big
magnet" to use, so I (intentionally) did not
exclude the use of a big, AC electromagnet.

Second, its not at all clear to me why
magnetizing a whole tape uniformly (even if
that were possible using a big permanent
magnet) would render it unusable, any more
than magnetizing selected parts of it (by,
say, writing data to it normally) would. But
perhaps there's something fundamental about
magnetic tape recording which I don't
understand. (Or at least one of us doesn't.)

> [...] (first hand experience).

My first-hand experience differs from yours.

I sure do enjoy the folklore, but, as before,
if you could offer a credible reference for
this claim, too, then it might be more
plausible. (But I suspect that this one's
about as good as the previous one.)

[Bill Hassell]

http://www.dw-world.de/staticfiles/pdf/dwfz/Magnetic_Sound_Recording.pdf

Section 4.5.2 (and others) explain the effects of DC bias, caused by permanent magnet fields. Recording heads cannot create a strong enough field to overcome this residual magnetism.

[Steven Schweda]

When did we change the discussion topic to
Magnetic _Sound_ Recording? When dealing
with zeros and ones, rather than audio
waveforms, concepts like distortion and noise
lose much utility.

Is this what worried you?:

DC magnetization on a recorded tape
cannot be removed and increases the
noise level permanently.

What that actually means is that any DC bias
in an audio recording can't be removed
>>without erasing the recorded audio<<. It
does _not_ mean that the tape can never be
demagnetized.

> [...] Recording heads cannot create a
> strong enough field to overcome this
> residual magnetism.

Says who? I believe that you're mistaken.
(He said, trying to avoid prohibited personal
abuse.) An _audio_ recording head may not
normally be driven hard enough to saturate
the tape, because one normally tries to keep
an audio signal within the (roughly) linear
range of the medium. In digital recording
(as with an audio erase head) this kind of
limit does not apply.

That document appears to contain considerable
valuable information, but pulling some
irrelevant warning out of its middle does not
constitute a wise use of a potentially
valuable resource. But if you find any
reliable information which is also relevant,
then please let us know. (Something about
recording digital data on a magnetic medium,
for example.)