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From: aslater@jocko.bri.hp.com ()
Subject: Re: HP C1533A DAT tape ?
Sender: news@bri.hp.com (News User)
Message-ID: <E03n06.8yw@bri.hp.com>
Date: Wed, 30 Oct 1996 17:24:06 GMT
Reply-To: aslater@jocko.bri.hp.com
References: <stanbDzLuJv.CEo@netcom.com> <Dzrx1z.9xv@bri.hp.com> <54rce7$9ta@uriah.heep.sax.de> <stanbDzw2rz.6yz@netcom.com> <E03118.Fo@bri.hp.com>
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Organization: Hewlett-Packard
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aslater@jocko.bri.hp.com wrote:
: Stan Brown (stanb@netcom.com) wrote:
: : j@uriah.heep.sax.de (J Wunsch) writes:
: : >aslater@jocko.bri.hp.com () wrote:
: : >> : If I can, what device should I use ? Will this device enable
: : >> : the compresion on the tape drive ?
: : >> 1. hack st.c and put in relevant quirks / code to get yourself DC control
: : >> by device file used (code for this isn't hugely difficult)
: : >Ah, it's even simpler. :)
: : >Try the `mt comp 1' command. I've just checked, it's around there at
: : >least since FreeBSD 2.0.5. The man page still lies that it were not
: : >implemented though... but i cannot remember a single feedback whether
: : >it's actually working now. It has been implemented blindly after the
: : >SCSI-2 specs by Julian Elischer.
: : Well, since I have the hardware handy, I'll check it :-) Can
: : anyone think of a way to check to see whether the tape s really being
: : writeen with compression (assuming I don't have ahandy data set bigger
: : than the uncompressed tape size ? Would backing it up and trying to read
: : it on a non-compression drive work ? I have one of those at work, and I
: : seem to remember ocasianly geting read failures on tapes in it.
: : Whe I put these tapes in the comprresion mode drive the read OK.
: : Does this make sense ?
: Time it.
: Try backing up (assuming you are backing something thats moderately
: compressible) as is with the software compression on (mt command as
: above). Then try doing same with it off. Should be faster with on.
: You can also try.... play with the two dips underneath and see what speed
: you get.
: If you change the dips thus...
^ first two.
: 11 DC on by default, host control on
: 10 DC on by default, host control off
: 01 DC off by default, host control on
: 00 DC off by default, host control off
: Where host control on means that the host can ask to turn DC on/off in
: software.
: It should be noticeably different. There's a host of other stuff you could
: do like dinging the DC page and seeing what compression ratio you're
: getting, etc.
: regards,
: al
: (not speaking for HP..)