Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!rlgvax!hadron!jsdy
From: jsdy@hadron.UUCP (Joseph S. D. Yao)
Newsgroups: net.unix-wizards
Subject: Re: Ultrix dump to TK50 not using entire tape?
Message-ID: <342@hadron.UUCP>
Date: Thu, 27-Mar-86 23:31:45 EST
Article-I.D.: hadron.342
Posted: Thu Mar 27 23:31:45 1986
Date-Received: Sat, 29-Mar-86 16:20:48 EST
References: <257@cirl.UUCP>
Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao)
Distribution: net
Organization: Hadron, Inc., Fairfax, VA
Lines: 23
Summary: Use undocumented keys.  [;-}]

In article <257@cirl.UUCP> das@cirl.UUCP (Dave Steffens) writes:
>We are running Ultrix version 1.1 on a uVAX II with TK50 cartridge tape drive.
>When dumping our main filesystem to TK50 tape, we noticed that each cartridge
>appears to hold only about 40Mb instead of its rated capacity of 95Mb.
>What's going on here?

The default for dump is to assume size 2300', 1600 bpi, blocking of
10 (*1024), 9-track magnetic tape.  This gives us 27600" of tape,
with 10240 bytes/tape block, or 6.4" + 0.7" IRG (InterRecord Gap).
27600/7.1 ~= 3887.324 10K blocks, or ~38.87 Mb.  Several ways out
include (documented) key B to tell it how many K long the tape
really is; or (undocumented) key 'c', which sets all the parameters
correctly for a cartridge.  (Another undocumented key is 'b', to
change the blocking factor.  Use 'c'.)  Let me know whether 'c' also
increases your speed/efficiency.

[The above formulae assume 1600 bpi 9t => 1 byte/linear bit space.]

This is under Ultrix 1.1 on a VAX; I'm assuming similar code for
your uVAX II.  The kernel code is the same.
-- 

	Joe Yao		hadron!jsdy@seismo.{CSS.GOV,ARPA,UUCP}