linux-kernel - Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

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Date:	Tue, 19 Jun 2007 10:11:13 +0100
From:	Pádraig Brady <P@...igBrady.com>
To:	Vladislav Bolkhovitin <vst@...b.net>
CC:	Chris Mason <chris.mason@...cle.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

Vladislav Bolkhovitin wrote:
> 
> I would also suggest one more feature: support for block level
> de-duplication. I mean:
> 
> 1. Ability for Btrfs to have blocks in several files to point to the
> same block on disk
> 
> 2. Support for new syscall or IOCTL to de-duplicate as a single
> transaction two or more blocks on disk, i.e. link them to one of them
> and free others
> 
> 3. De-de-duplicate blocks on disk, i.e. copy them on write
> 
> I suppose that de-duplication itself would be done by some user space
> process that would scan files, determine blocks with the same data and
> then de-duplicate them by using syscall or IOCTL (2).
> 
> That would be very usable feature, which in most cases would allow to
> shrink occupied disk space on 50-90%.

Have you references for this number?
In my experience one gets a lot of benefit from
the much simpler process of "de-duplication" of files.

Note a checksum stored in file metadata,
that is automatically invalidated on write would
speed up user space file de duplification,
and rsync, etc....

Pádraig.
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