SCSI tape question

[Jon Elson]

On 12/13/2014 01:36 AM, John Wilson wrote:
> On Fri, Dec 12, 2014 at 11:04:20PM -0600, Jon Elson wrote:
>> I worked with some Exabyte
>> drives and others that had a lot of constraints on what you could do,
>> and you could do some interesting things.
> My recollection with the Exabyte 8mm drives was that they would let you
> write new data after the last thing written, but you couldn't backspace and
> write over existing data, unless you were rewinding all the way to BOT.  So
> they were lousy at emulating 9-tracks (but some controllers fixed that by
> wrapping everything in headers and writing their own suffix records that
> said when to disregard the last N blocks, and they'd read ahead by some
> known amount looking for that, to at least handle the common case of going
> to LEOT, backspacing between the two tape marks, and writing a new file).
No, you could commence writing after any existing record, 
and the drive would take
care of the mess that was similar to a punch-in edit on 
videotape, if you remember
what that looked like on the early VCR's.  It would just 
overwrite the following data
for about 2-3 seconds with full-width erase, and then pick 
up writing in cleanly-erased
tape.  I think some of the later drives might have been able 
to do better with flying
erase heads.  But, we generally never did fancy stuff with 
them, just write a whole
tape at a time.  Anyway, we never added records to an 
existing file, but did often
add new files after the double file mark.

Jon