tlz04 density

[Allan E Johannesen]

On 17 May 91 07:52:40 GMT,
olson at anchor.esd.sgi.com (Dave Olson) said:
olson> Sender: news at odin.corp.sgi.com (Net News)

olson> There are no interrecord gaps on DAT tapes.  That isn't the way
olson> they work.  It doesn't really matter what block size you use,
olson> as long as it is a multiple of 512 bytes, aside from OS
olson> efficiency issues.

This is interesting.  I no nothing of the DAT technical details; I
just considered myself lucky to be able to obtain one.  Lacking any
guidelines for dump, I wrote a stupid program which writes blocks
until it gets an error, then prints the block count.

For 10,240 byte blocks (the size which DECstations write during dump
and rdump), I found I could write 107,528 blocks, thus 1,101,086,720
bytes.

At a 32,768 byte blocksize (the size used by a different UNIX box
during rdump), I found could write 39,792 blocks, or 1,303,904,256
bytes.

I did no other experiments, having no other uses for the drive.

I had assumed there was some IRG-similar situation at work here, since
~10% more data will fit at the larger blocksize; since this is
apparently not due to gaps, it must be due to something else.