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From: mike@erix.UUCP (Mike Williams)
Newsgroups: net.unix
Subject: Block size on dumps (4.2BSD)
Message-ID: <735@erix.UUCP>
Date: Mon, 4-Feb-85 14:08:59 EST
Article-I.D.: erix.735
Posted: Mon Feb  4 14:08:59 1985
Date-Received: Fri, 8-Feb-85 02:06:33 EST
Organization: L M Ericsson, Stockholm, Sweden
Lines: 16

Dump uses blocks of NTREC (defined in ) * 1024 bytes.
NTREC is defined as 10. For 1600 bpi this gives a tape "usage"
of about 90% (assuming that a block gap is 0.6 of an inch). 

However at 6250 bpi this becomes about 70% which is not so good. (ie I 
can't get a 130 Mbyte partition onto one tape). I tried increasing NTREC
to 20 and checked that dump and restore still worked, which they did.
NTREC of 20 gives about 84% usage. To get up to the 90% at 1600 bpi
you have to increase NTREC to 40. 

Having larger blocks increases the danger of a bad patch spoiling more of 
the dump, but are there any other obvious disadvantages?

Mike Williams
{decvax,philabs}!mcvax!enea!erix!mike or mike@erix.UUCP