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From: Mel Flynn <mel.flynn+fbsd.questions@mailing.thruhere.net>
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Date: Mon, 10 Aug 2009 19:08:35 -0800
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Cc: Roland Smith <rsmith@xs4all.nl>, Jay Hall <jhall@socket.net>
Subject: Re: Backup Size
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On Monday 10 August 2009 18:24:19 Jay Hall wrote:
> On Aug 10, 2009, at 12:09 PM, Roland Smith wrote:
> >> The fact that you are using tar also plays a part. Tar has some
> >> overhead to
> >> store information about the files it contains.
>
> Is it possible to calculate the amount of overhead tar will use?

Difficult. 512 bytes per entry + 1024 (EOF). See man 5 tar. But since files 
will be padded there is some extra overhead. Also, it is hard to calculate 
hard links and sparse files. Tar will handle these correctly (i.e. preserve 
hard links and detect sparse files and try not archive "blocks of nulls") but 
it is hard to calculate the size because of this before the archive operation 
because of this.
-- 
Mel