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Date:      Sun, 1 Feb 2009 18:31:28 +0000
From:      RW <rwmaillists@googlemail.com>
To:        freebsd-questions@freebsd.org
Subject:   Re: dump(8) using snapshot + "recommended" cache
Message-ID:  <20090201183128.524f16db@gumby.homeunix.com>
In-Reply-To: <alpine.BSF.2.00.0902010838030.1180@qemg.org>
References:  <alpine.BSF.2.00.0902010838030.1180@qemg.org>

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On Sun, 1 Feb 2009 08:59:02 -0400 (AST)
Andrew Hamilton-Wright <andrewhw@ieee.org> wrote:

> 
> Hi All;
> 
> I regularly use dump(8) with snapshots to back up my server.
> 
> While this seems to have been working perfectly well so far,
> upon (re)reading the man page for dump(8), I have noticed a
> somewhat scary pair of lines in the paragraph describing
> the option for -C <cachesize> (emphasis with stars mine):
> 
>  	[Use of this option] will greatly improve performance
>  	at the cost of ***dump possibly not noticing changes in
>  	the file system*** between passes.
> 
>  	***It is recommended that you always use this option when
>  	dumping a snapshot.***
> 

When you dump a snapshot there are, by definition, no changes between
passes. So it's saying that in that case there in no reason not to
cache. 



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