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From: burgess@s069.infonet.net (Dave Burgess)
Newsgroups: comp.os.386bsd.questions
Subject: Re: dump parameters for HP 35480 DAT drive
Date: 20 Jun 1994 22:13:42 -0500
Organization: Dave's House in Omaha
Lines: 61
Message-ID: <2u5lt6$hc@s069.infonet.net>
References: <Crpn94.21B@luva.stgt.sub.org>
NNTP-Posting-Host: s069.infonet.net
In article <Crpn94.21B@luva.stgt.sub.org>,
Michael Giegerich <migieger@luva.stgt.sub.org> wrote:
>
>Hi,
>
>I have this little gem of DAT drive and can't force it to do
>what I want, grrrr...
>
>I found out that the drive uses 61000 bpi media, but a 90 m
>(295 feet) cartridge gives me 295*12 in * 61000 bpi = about 200 MB.
>
Yup; the tape densities are pretty meaningless. If you multiply your
raw number above by 8 or 9, it gets about right...
>Much lesser than the 2 GB uncompressed and the 8 GB compressed
>data a cartridge should hold (yes I know, that's unlikely to stuff
>8 GB of gzip'ed code onto the cartridge).
>
>So I'm puzzled what tape length I must give to dump as parameter...
>And is it up to me to _guess_ what is the tape length parameter
>with compression enabled?
I am using 1020 foot DC6250 cartiridges in my wt0 drive. I finally
settled on 11200 bpi and 1000 feet for a close approximation.
The box says 12500 bpi, but that is too much away from the real amount
of tape used. Note that the numbers I got (11200 * 1000) mean that I
should only get about 11 Meg per cart, off by a factor of 9...
I used the trial and error method. I backed up until I got a full
tape, and then played around with the densities and lengths until the
file system got to about the right amount of tape used.
>
>One friend told me "I'm using a ridiculous high tape length on a
>Sun to fake unlimited tape - with the disadvantage that I must be
>sure I haven't to change tape" :-(
>I would consider this only as 2nd best choice...
>
Actually, it isn't a completely bad way to go. The numbers I was using
on the Sun I was working with in Texas had a really HUGE number. It
actually computed out about right, but it was still a realtively
enormous number.
>
>P.S. Please give the apropriate restore commands and the /dev to
> use too (it saves me endless tries and errors). Thanks.
I would guess that your tape drive is a SCSI DAT drive, so it should be
something like /dev/rst0 or /dev/rst1. If not, you're on your own :-).
--
TSgt Dave Burgess | Dave Burgess
NCOIC, USSTRATCOM/J6844 | *BSD FAQ Maintainer
Offutt AFB, NE | Burgess@cynjut.infonet.net or ...@s069.infonet...