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From: rct@occrsh.UUCP
Newsgroups: net.unix-wizards
Subject: Re: Tar(1) portability???
Message-ID: <4500001@occrsh.UUCP>
Date: Fri, 10-Jan-86 23:01:00 EST
Article-I.D.: occrsh.4500001
Posted: Fri Jan 10 23:01:00 1986
Date-Received: Fri, 17-Jan-86 01:28:21 EST
References: <535@smeagol.UUCP>
Lines: 25
Nf-ID: #R:smeagol.UUCP:535:occrsh.UUCP:4500001:000:1160
Nf-From: occrsh.UUCP!rct    Jan 10 22:01:00 1986


One of the major problems with respect to portability of tar tapes
(in my experience) has been the tendency of well-meaning friends to
use the blocking factor 20 without realizing that, for Sys V tar anyway,
this results in a record length of 20 x 512 = 10k bytes.  Unfortunately,
the 3B20S computers I use have tape controllers (UN52) with a hardware
limitation of 6k bytes max record length, and 3B5 tape controllers are
scarcely any better with a limit of 8k bytes.  This is particularly
annoying when fellow administrators with VAXen tell me that they have
no problems using blocking factors exceeding 20k.  One such person said
that the ANSI standard (unknown) provides for blocking factors as high
as 32k!!

On the plus side, there is now (in the documentation at least) a
UN138 tape controller for the 3B20S that provides for maximum record
lengths of 30k bytes, as well as 1600/6250 densities.

SO...  In addition to any problems related to different tar versions,
you might be fighting tape controller limitations on maximum record
length as well.

--Bob Tracy	AT&T Technologies, Inc.		Network Systems
  Oklahoma City, OK

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