Date: Wed, 28 Aug 1996 23:26:19 +0000 From: Darius Moos <moos@degnet.baynet.de> To: FreeBSD-questions <questions@freebsd.org> Cc: freebsd-hackers <freebsd-hackers@freebsd.org> Subject: [Q]: formula for calculating BPI needed Message-ID: <3224D59B.74DF@degnet.baynet.de>
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Hi,
My first basic question is, how one would calculate the BPI
for a given DAT-tape-length and capacity. My problem is:
- let a DAT-tape be 295 feet long <=> lf = 295
=> length of this DAT-tape is li = lf * 12 = 3540 inches
- let the capacity of this tape be 2 GB
=> BPI = 2 GB / li = 2 GB / 3540 inches = 606633.8 BPI
The maual i've read says the BPI is 61000 for such a tape.
So what am i doing wrong ?
i was trying to dump filesystems to a SONY-SDT-7000 with dump.
My problem is, that dumps estimated tapes for the dump are wrong;
for example dumping /dev/sd0a (about 50 MB) to a 295 feet long
DAT-tape makes dump to estimate 0.4 tapes (i set the commandlineoptions
to "0ufds /dev/sd0a 61000 295"). This can not be correct,
since the capacity of a 295 feet-DAT-tape is about 2 GB.
After scanning the sources of dump for the estmated-tapes-formula,
i found some strange constants being used there that i do not
understand and that are not documented nor explained anywhere.
I want to rewrite the formula for this calculation in
the dump-sources but i need some informations on this topic.
Maybe there is someone out there willing to give me some assistence
in understand what is going on in the dump-formula.
Many thanks in advance for all your help.
Bye, Darius.
email: moos@degnet.baynet.de
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