Date: Wed, 28 Aug 1996 17:16:52 -0700 (PDT) From: "Jonathan M. Bresler" <jmb> To: moos@degnet.baynet.de Cc: questions@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: [Q]: formula for calculating BPI needed Message-ID: <199608290016.RAA15559@freefall.freebsd.org> In-Reply-To: <3224D59B.74DF@degnet.baynet.de> from "Darius Moos" at Aug 28, 96 11:26:19 pm
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Darius Moos wrote: > > 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 ? trying to use bpi for a DAT tape ;) bpi is from the days of 9-track tapes. use B and b instead. B -- number of dump records b -- number of kilobytes per dump record. for a 2GB tape try 500000 40 dump Bbf 500000 40 /dev/rst0 <filesystem> > > 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, the trick there is helical scan. the bpi may acutally be 61000. that 61000 bpi are recorded at an angle of ~6 degrees from horizontal. the width of hte recorded path is very narrow. many recording paths lie stacked above one another. similar to repeated slash symbols at a shallower angle "////" as a result the effective length of a tape is increased many-fold. > 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. no, you dont ;) well maybe you do but others dont want you to :) the formulas in dump are there for the old 9-track tapes. just use the newer parameters: B and b. jmb -- Jonathan M. Bresler FreeBSD Postmaster jmb@FreeBSD.ORG FreeBSD--4.4BSD Unix for PC clones, source included. http://www.freebsd.org/ PGP 2.6.2 Fingerprint: 31 57 41 56 06 C1 40 13 C5 1C E3 E5 DC 62 0E FB
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