Re: Copy on write of unmodified data

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On Wed, May 25, 2016 at 01:58:15AM -0700, H. Peter Anvin wrote:
> Hi,
> 
> I'm looking at using a btrfs with snapshots to implement a generational
> backup capacity.  However, doing it the naïve way would have the side
> effect that for a file that has been partially modified, after
> snapshotting the file would be written with *mostly* the same data.  How
> does btrfs' COW algorithm deal with that?  If necessary I might want to
> write some smarter user space utilities for this.

   Sounds like it might be a job for one of the dedup tools
(deupremove, bedup), or, if you're writing your own, the safe
deduplication ioctl which underlies those tools.

   Hugo.

-- 
Hugo Mills             | Well, sir, the floor is yours. But remember, the
hugo@... carfax.org.uk | roof is ours!
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                             The Goons

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