On Thu, 27 Jul 2000, Brian wrote:

> I found the 8mm we use for AS/400 backups here.  It's a "helical scan"
> whatever that means, but my 112m tape holds 2.5/5 GB, so if I math it out
> (assuming it's linear) 160m should be somwhere around 3.5-4 GB uncompressed.
> Is it possible that your drive will only take a 2/4 GB tape (either by
> design or by "unfortunate incident")?

That's a drive thing.  112m is what the Exabyte 8500C can get 5GB onto
uncompressed.

Still, you're right, Bob should be able to get more than 2GB on a 160m
tape.

BTW, helical scan means that it's a rotating head, like in a VCR.  Instead
of writing the tracks longitudinally along the tape, they are written by a
head that is spinning, but at an angle to the tape, creating a bunch of
segments that have been arranged like "angle parking," just like a row in
the parking lot.

Cheers,

Phil M
 
> On Wed, 26 Jul 2000, Philip C Mendelsohn wrote:
> 
> > On Wed, 26 Jul 2000, Bob Tanner wrote:
> >
> > > Running Sparc Linux with a Exabyte 8mm Tape drive using 160mXL 8mm
> tapes.
> > >
> > > I think I am going insane, but I thought 8mm did 12/24Gb. Yet, I am able
> only
> > > to get around 2Gb on the tape before it gives me a write error.
> > >
> > > Just wanted to make sure my capacity is right on the tapes before I look
> else
> > > where.
> >
> > Depends on the drive, but that's *way* higher than what I would expect.
> >
> > I have an Exabyte 8500C, which is rated for 5GB uncompressed, 10GB with
> > the hardware compression.  (It's older, but it's a rock.)
> >
> > I don't recall if that was 160m tapes or not, but the difference for tape
> > length is linear, so that doesn't explain it.
> >
> > 2GB is pretty shabby though.
> >
> > There are lots of annoying problems that could account for it -- bad
> > tapes, dirty machines, yada, yada.  I have a fair amount of insight into
> > the behavior of tapes and heads which I won't burden you with now :)
> >
> > I don't want to start a "I swear by brand X, but brand Y
> > stinks" discussion, but I have some data on error rates, bad tapes
> > received, and recoverability after time that suggests that the 3M /
> > Imation 8mm tapes really do outperform a couple of other brands.
> >
> > *I'm not claiming they beat everyone else's tape.*
> >
> > Nutshell:  Your numbers probably aren't right, but your tape is *almost*
> > certainly not doing what it's supposed to, IMHO.
> >
> > Cheers,
> > Phil M
> >
> > --
> > Lottery:    a tax on people who are bad at math
> >
> >
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-- 
Lottery:    a tax on people who are bad at math


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