Re: Possible to dedpulicate read-only snapshots for space-efficient backups

[Kai Krakow <hurikhan77+btrfs@gmail.com>]

Gabriel de Perthuis <g2p.code@gmail.com> schrieb:

> It sounds simple, and was sort-of prompted by the new syscall taking
> short ranges, but it is tricky figuring out a sane heuristic (when to
> hash, when to bail, when to submit without comparing, what should be the
> source in the last case), and it's not something I have an immediate
> need for.  It is also possible to use 9p (with standard cow and/or
> small-file dedup) and trade a bit of configuration for much more
> space-efficient VMs.
> 
> Finer-grained tracking of which ranges have changed, and maybe some
> caching of range hashes, would be a good first step before doing any
> crazy large-file heuristics.  The hash caching would actually benefit
> all use cases.

Looking back to good old peer-2-peer days (I think we all got in touch with 
that the one or the other way), one title pops back into my mind: tiger-
tree-hash...

I'm not really into it, but would it be possible to use tiger-tree-hashes to 
find identical blocks? Even accross different sized files...

Regards,
Kai