🚀 go-pugleaf

[cross-posted to comp.periphs.scsi where someone will know
this stuff better than I and hopefully correct any errors here.]

In article <4g0e77$1v7e@usenetw1.news.prodigy.com> bill davidsen
(davidsen@tmr.com) wrote:

>In article <TT.96Feb10182535@tarzan.jyu.fi>,
>Tapani Tarvainen <tt@tarzan.jyu.fi> wrote:

>| Partitions are fundamentally different from setmarks/filemarks in that
>| you can write to either partition without disturbing the other, in any
>| order, any number of times.  Very useful in some situations.

>I'm still missing something. If I write, say, 500M on a DAT tape,
>and then a set mark, I can then rewind the tape and write what I
>want without disturbing the data past the set mark,

Nope.  Whenever you write something on a DDS (DAT) tape, everything
after that point is lost, up to the end of tape *or partition*.
Stuff on the other partition (if any) won't be affected.

>or space to the set mark and write data without affecting the stuff
>at the start of the tape.

Yes.

>If I partition a tape and start writing at the beginning, will I get
>an end of tape status at the end of the partition, or waste the
>divider? 

The former.  A partitioned tape looks like two tapes; to a program
(driver) that doesn't understand partitions it'll probably look
like a short tape, i.e., the second partition will be invisible.
There is no easy way to get rid of the partition divider:
you'll have to format the tape -- and indeed just about the only
situations when you'll need to format DDS tapes is when you want
to partition a tape or destroy/modify partitioning.

>I assume that can be done at the driver level only if the
>hardware supports it at least a little.

I believe the support is required by DDS standard (not sure
about that, though).

-- 
Tapani Tarvainen