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

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Date:	Mon, 18 Jun 2007 21:37:26 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

Chris Mason wrote:
> Hello everyone,
> 
> After the last FS summit, I started working on a new filesystem that
> maintains checksums of all file data and metadata.  Many thanks to Zach
> Brown for his ideas, and to Dave Chinner for his help on 
> benchmarking analysis.
> 
> The basic list of features looks like this:
> 
> 	* Extent based file storage (2^64 max file size)
> 	* Space efficient packing of small files
> 	* Space efficient indexed directories
> 	* Dynamic inode allocation
> 	* Writable snapshots
> 	* Subvolumes (separate internal filesystem roots)
> 	- Object level mirroring and striping
> 	* Checksums on data and metadata (multiple algorithms available)
> 	- Strong integration with device mapper for multiple device support
> 	- Online filesystem check
> 	* Very fast offline filesystem check
> 	- Efficient incremental backup and FS mirroring

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%.

Vlad
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