[Coco] LSN0 C code

[gene heskett]

On Saturday, June 11, 2011 12:37:51 PM Steven Hirsch did opine:

> On Sat, 11 Jun 2011, gene heskett wrote:
> > We had, past tense, a bulk eraser at the tv station that was
> > apparently made for erasing the 10.5" and 14" NAB reels of audio
> > tape.  But it fell into disuse when the 3/4" u-matic format for video
> > came along as it was not strong enough to wipe all the way to the
> > center.
> > 
> > Somewhere in my collection I have one of the hand held ones that the
> > Shack sold for cassette tapes, and it worked well on floppies,
> > including 3.5".
> > 
> > For audio work, it is very important that the media be removed very
> > slowly from the field these generate before the power switch is
> > released.  Turn it off while the tape is still in contact, and you
> > likely will leave the tape very hissy & noisy, with a distinct, it
> > will peg the vu meters thump once per turn of the reel.
> 
> As effective as those gadgets are on audio and video tape, they do not
> typically generate enough field strength to wipe linear digital media.
> It was eye-opening to run a DLT IV cartridge over my trusty, 40-year-old
> Nortronics desktop eraser and discover that it remained readable!
> 
> A link off that UTube page leads to an industrial-strength unit that is
> designed for DLTs.  I'm not asking, because I'm sure I cannot afford it
> 
> :-).
> 
> FYI: DLT drives write their own servo information as they go and are
> designed to work with blank media.  The newer (and physically similar)
> LTO format has a factory-written servo track and will be destroyed
> completely by a capable eraser.  I'm sure a number of users have
> discovered this the hard way when they ruin a $40.00 cartridge.
> 
> Steve

Yes, I've managed to wipe out both a DDS-2, and a couple of Travan 
cartridges before I discovered that.  For both, I was trying to disable the 
drives compression flag, which once turned on, cannot generally be turned 
off by any normal drive command.

I found the secret is to use dd to read the first 32k block out to a file, 
rewind the tape, issue the compress off command without giving the drive a 
chance to re-read the header, then, again using dd, rewrite that label 
header, which will force most drives to update that (&^$#@) flag to off.  
GZip can very easily beat the drives compression ratio, and since amanda 
counts bytes sent down the cable, it knows how much it was written to that 
tape.  I when tape limited, routinely filled a tape to 98% without every 
hitting the EOT signal.  Now I use a big hard drive as 30 virtual tapes and 
don't worry about it.

Cheers, gene
-- 
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-Ed Howdershelt (Author)
I cannot draw a cart, nor eat dried oats; If it be man's work I will do it.