Re: dduper - Offline btrfs deduplication tool

[Zygo Blaxell <ce3g8jdj@umail.furryterror.org>]

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On Fri, Sep 07, 2018 at 09:27:28AM +0530, Lakshmipathi.G wrote:
> > 
> > One question:
> > Why not ioctl_fideduperange?
> > i.e. you kill most of benefits from that ioctl - atomicity.
> > 
> I plan to add fideduperange as an option too. User can
> choose between fideduperange and ficlonerange call.
> 
> If I'm not wrong, with fideduperange, kernel performs
> comparsion check before dedupe. And it will increase
> time to dedupe files.

Creating the backup reflink file takes far more time than you will ever
save from fideduperange.

You don't need the md5sum either, unless you have a data set that is
full of crc32 collisions (e.g. a file format that puts a CRC32 at the
end of each 4K block).  The few people who have such a data set can
enable md5sums, everyone else can have md5sums disabled by default.

> I believe the risk involved with ficlonerange is  minimized 
> by having a backup file(reflinked). We can revert to older 
> original file, if we encounter some problems.

With fideduperange the risk is more than minimized--it's completely
eliminated.

If you don't use fideduperange you can't use the tool on a live data
set at all.

> > 
> > -- 
> > Have a nice day,
> > Timofey.
> 
> Cheers.
> Lakshmipathi.G

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