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Date:      Sun, 10 Sep 2006 21:05:48 +0100
From:      Alex Zbyslaw <xfb52@dial.pipex.com>
To:        Bob <bob@tania.servebbs.org>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: SnapShot Magic
Message-ID:  <4504701C.6090104@dial.pipex.com>
In-Reply-To: <200609101426.52892.bob@tania.servebbs.org>
References:  <200609101426.52892.bob@tania.servebbs.org>

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Bob wrote:

>/usr is a 33GB HW/Raid  partition, how can it possibly hold 6 33GB 
>snapshots???
>
>If I mount each one of these, they all report to df that they are indeed 33BB 
>file systems!
>
>How is this magic achieved? 
>
>Is there a doc somewhere with an explaination?
>  
>
Snapshots only hold the originals of blocks that have changed, but still 
look like a complete file system when you mount them.

 From man mount:

>                         Further details can be found in the file at
>                          /usr/src/sys/ufs/ffs/README.snapshot.
>  
>
which should have a pointer to the original paper.

--Alex





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