From: Bruce Guenter <bruce@untroubled.org>
To: linux-btrfs@vger.kernel.org
Subject: Re: is space really freed after deleting large subvolume?
Date: Fri, 14 Oct 2011 11:12:29 -0600 [thread overview]
Message-ID: <20111014171229.GA7528@untroubled.org> (raw)
In-Reply-To: <20111014084504.GI21931@carfax.org.uk>
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On Fri, Oct 14, 2011 at 09:45:05AM +0100, Hugo Mills wrote:
> Updating and checking the reference count is the thing
> that takes time, and can't really be short-circuited.
I'm curious if you know how ZFS does this. My boss has used a set of
ZFS systems for backup, and indicates that deleting a snapshot is
instant, and free space is updated immediately with no apparent
background I/O. I know ZFS only has read-only snapshots, but I would
think it would have some of the same reference counting challenges.
I see reading one of the ZFS presentations that it uses a "birth time"
in each block pointer. This lets it optimizes the deletion by walking
only a partial set of the nodes. Still, for any non-trivial deletion it
would have to walk enough nodes to keep the delete from being as quick
as is claimed.
--
Bruce Guenter <bruce@untroubled.org> http://untroubled.org/
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prev parent reply other threads:[~2011-10-14 17:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-13 16:14 is space really freed after deleting large subvolume? krzf83@gmail.com
2011-10-13 16:21 ` Hugo Mills
2011-10-13 16:57 ` krzf83@gmail.com
2011-10-13 18:06 ` krzf83@gmail.com
2011-10-13 19:22 ` krzf83@gmail.com
2011-10-13 20:01 ` David Pottage
2011-10-13 21:03 ` krzf83@gmail.com
2011-10-14 17:26 ` Maciej Marcin Piechotka
2011-10-13 16:29 ` Roman Mamedov
2011-10-14 5:17 ` krzf83@gmail.com
2011-10-14 8:45 ` Hugo Mills
2011-10-14 17:12 ` Bruce Guenter [this message]
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