Dumping to an exabyte tape drive

[Dave Martindale]

On 4 Sep 90 17:02:28 GMT, rsb1 at cbnewsk.att.com (richard.s.brown) said:

> We use 120 min tapes. We bought our drives from Perfect Byte,
> Inc.	in Omaha, Nebraska. The documentation we received was
> remarkably good (and concise!) Here are the suggested values for
> 'dump':

> 		Blocking factor:	126
> 		Density:		54000 (bpi!!!)
> 		Length:			6000 (ft.)

Yes, that's what the Perfect Byte manual says, but they're wrong.

The blocking factor is fine; 126 (512-byte) blocks is the largest
transfer you can do to an Exabyte on a Sun and still have the block
size a multiple of 1024.  (1024 bytes is the Exabyte's own internal
block size).

However, the density and length figures, when multiplied together,
tell "dump" that you can fit 3.8 Gb on a tape.  Dump will reduce that
somewhat by allowing for inter-record gaps (which are nonexistent
on 8mm tape), but I think you'll find that dump will hit the Exabyte's
end-of-tape while it thinks there is more tape left.

Now, if all of your dumps will fit on one Exabyte tape anyway, this
is fine - all you really have to do is convince dump that the tape
is bigger than the amount of data that is to go on it.  However, if
you have enough data to take more than one tape, you'll have to
calculate the real size of the tape more accurately.