🚀 go-pugleaf

Is there anyone who can explain this:

We use an exabyte 8505 on sunos4.1.3.
We use (r)dump to make a backup with the following (conservative)
parameters from when we still had 8200's
	rdump bsdfu0 100 6000 50000 ....
Dump tells us:
	DUMP: estimated 3444210 blocks (1681.74MB) on 1.06 tape(s).
Why should it only store 1.6GB on a 2.3GB tape?

I go and check:

Sun advices the following parameters:
#    "8mm",  "bdsf   112  54000  6000   : 2.3G", # Exabyte 8200
#    "8mm2", "bdsf   112 108000  6000   : 5.2G", # Exabyte 8500 (double
density)
#    "8mm4", "bdsf   112 216000  6000   :10.4G", # Exabyte 8500-Compression

That is some 8% more space on the tape than we assumed.

Then i calculate:

54000 bpi * 6000 ft * 12 i/ft = 3888000000 bytes = 3.62 GB
(i do not know how much tapeloss i need to calculate for the interrecord gaps)

And because I want the backup done i do (it IS an 8505 right?):

	rdump bsdfu0 100 6000 100000 ... ...
	 ...
	DUMP: estimated 3448954 blocks (1684.06MB) on 0.82 tape(s).

So doubling the density increases the capacity by 30%??

What is going on, what am i missing??
I would think that i could get the numbers somewhat identical.
-- 

tom ploegmakers		NIKHEF-CT	(tom@nikhef.nl)	
			po.box 4395, 1009 AJ Amsterdam, the Netherlands.
			phone: -31 20 5922035