Date: Tue, 19 Jun 2007 11:24:30 -0700 (PDT)
From: david@lang.hm
To: Chris Mason <chris.mason@oracle.com>
cc: =?iso-8859-1?Q?P=E1draig?= Brady <P@draigBrady.com>,
       Vladislav Bolkhovitin <vst@vlnb.net>, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS
In-Reply-To: <20070619120457.GD14108@think.oraclecorp.com>
Message-ID: <Pine.LNX.4.64.0706191121260.25045@asgard.lang.hm>
References: <20070612161029.GB28279@think.oraclecorp.com> <4676C2D6.8030708@vlnb.net>
 <46779DB1.7060807@draigBrady.com> <20070619120457.GD14108@think.oraclecorp.com>
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On Tue, 19 Jun 2007, Chris Mason 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?
>> In my experience one gets a lot of benefit from
>> the much simpler process of "de-duplication" of files.
>
> Yes, I would expect simple hard links to be a better solution for this,
> but the feature request is not that out of line.  I actually had plans
> on implementing auto duplicate block reuse earlier in btrfs.

with COW de-duplication you can merge things that have vastly different 
permissions. hard-links can't be used if different people have write 
permission.

David Lang

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