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From: Robert Watson <rwatson@freebsd.org>
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To: Peter Jeremy <PeterJeremy@optushome.com.au>
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cc: Christoph Kukulies <kuku@physik.rwth-aachen.de>
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Subject: Re: .fsck_snapshot file
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On Tue, 2 Sep 2003, Peter Jeremy wrote:

> On Tue, Sep 02, 2003 at 08:27:00AM +0200, Christoph Kukulies wrote:
> >I have a file .fsck_snapshot in /usr (of 7 GB ?!)
> >-r--------   1 root   wheel  7220781056 Aug 22 18:08 .fsck_snapshot
> 
> The '7GB' does not mean you'll free up 7GB of disk space by freeing it. 
> IIRC, it's actually the size of the filesystem. 

Although, as time goes by since the creation a snapshot, if you have a
fairly live file system, it will begin to approach it :-).  I've been
wondering if we ought to have some magic to GC these snapshots if/when
they are discovered during the boot or mount process just to be on the
safe side.  In theory, the window where the name exists is small (fsck
creates, opens, and immediately unlinks the snapshot).  Unfortunately, in
practice the window is apparently pretty wide since any system failure
during snapshot creation will (I believe) leave the snapshot reference
behind. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories