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

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Message-ID: <Pine.LNX.4.64.0706191118180.25045@asgard.lang.hm>
Date:	Tue, 19 Jun 2007 11:20:29 -0700 (PDT)
From:	david@...g.hm
To:	Vladislav Bolkhovitin <vst@...b.net>
cc:	Pádraig Brady <P@...igBrady.com>,
	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

On Tue, 19 Jun 2007, Vladislav Bolkhovitin wrote:

>> > 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?
>
> No, I've seen it somewhere and it well confirms with my own observations.
>
>>  In my experience one gets a lot of benefit from
>>  the much simpler process of "de-duplication" of files.
>
> Yes, sure, de-duplication on files level brings its benefits, but on FS 
> blocks level it would bring ever more benefits, because there are many more 
> or less big files, which are different as a whole, but with a lot of the same 
> blocks. Simple example of such files is UNIX-style mail boxes on a mail 
> server.

unix style mail boxes would not be a good example of wins for sector-based 
de-duplication since the duplicate mail is not going to be sector aligned.

David Lang

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