Path: utzoo!utgpu!watmath!mks!egisin
From: egisin@mks.UUCP (Eric Gisin)
Newsgroups: comp.unix.wizards
Subject: Re: GNU-tar vs dump(1)
Summary: beware sparse files
Message-ID: <629@mks.UUCP>
Date: 3 Jan 89 23:09:28 GMT
References: <17999@adm.BRL.MIL>
Organization: Mortice Kern Systems, Waterloo, Ont.
Lines: 10

One of the potential problems with using tar or cpio for backups
is that a sparse file (one with unallocated blocks)
that uses little disk space will use more space in the backup.
A sparse file can be created by a buggy program or by a user:
	$ adb -w big
	0t100000000?w0
	^D
	$ ls -ls big
	  24 -rw-r--r--  1 egisin   100000004 Jan  3 17:59 big
This file uses 24K on the BSD filesytem, and about 100M in a tar backup.