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

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Message-ID: <4678E81C.5000608@vlnb.net>
Date:	Wed, 20 Jun 2007 12:41:00 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	david@...g.hm
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

david@...g.hm 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.

Yes, I realized that after I sent the e-mail. Handling of the same, but 
not aligned, data in different files would need more complex logic. 
Maybe too complex.

Vlad
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