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

From: Vladislav Bolkhovitin
Date: Wed Jun 20 2007 - 04:41:46 EST

david@xxxxxxx 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.

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