[Info-vax] strange backup behavior

[AEF]

On Aug 11, 2:44 pm, glen herrmannsfeldt <g... at ugcs.caltech.edu> wrote:
> AEF <spamsink2... at yahoo.com> wrote:
>
> (snip)
>
> < I have a TZ88 and it seems to take a long time to get to the end of a
> < long save set. Have you checked? Why would the drive have 128 heads?
> < Sounds pretty expensive when one would do! (Actually, it has two. See
> < below from the TZ88 manual.
>
> < 1.4 Reading and Writing Data
> < The TZ88 Model 20/40 GB DLT Cartridge Tape Drive writes 64 pairs of
> < tracks ? 128
> < tracks total ? on the CompacTape IV tape. The drive reads and writes
> < data in a two-track
> < parallel, serpentine fashion, traveling the entire length of tape on
> < two tracks. The drive then
> < steps the head, reverses tape direction, and continues to read/write
> < on the next two tracks, repeating
> < this same process for a total of 64 times per tape.
>
> Yes.  But given a command to skip to a specific tape mark, the
> drive knows which track and approximately where on the tape that
> tape mark is.  The heads are moved to the appropriate track, and
> with an average of one half a pass through the tape the spot is found.

How does it know?

>
> For LTO, an EEPROM is used, for DLT data written by the drive
> before BOT.

I don't think we're talking about the same thing. If you are putting
multiple save sets on one tape, you don't need to rewind or skip
unless you use /verify, which the OP is not.

The only time one would need to do this is to find the EOT mark on a
tape that already has save sets on it when you put it in the drive.
Tell me how the tape drive is going to know what tracks the tape marks
are on when I go to my library (a drawer in a cabinet), pick some tape
at random, and put it in the drive.

>  In unix, one can do
>
> dd fsf 10
>
> to skip forward 10 tape marks.  

What does Unix have to do with it?

> If the software/hardware can do it,
> it will be done.

So it can be done; so it shall be done. So what? ;-)

AEF


>
> -- glen