On Wednesday 05 December 2007, redhat@xxxxxxxxxxx wrote:
> You'd think that using this technology on a live filesystem could incur a
> significant performance penalty due to all those calculations (fuse module
> anyone ?). Imagine a hardware optimized data de-duplication disk
> controller, similar to raid XOR optimized cpus. Now that would be cool. All
> it would need to store was meta-data when it had already seen the exact
> same block. I think fundamentally it is similar in result to on the fly
> disk compression.
Actually, the impact - if the filesystem is designed correctly - shouldn't be
that horrible. After all, Sun has managed to integrate checksums into ZFS and
still get great performance. In addition, ZFS doesn't directly overwrite data
but uses a new datablock each time...
What you would have to do then is keep a lookup table with the checksums to
find possible matches quickly. Then when you find one, do another compare to
be 100% sure you didn't have a collision on your checksums. If that works,
then you can reference that datablock.
It is still a lot of work, but as sun showed, on the fly compares and
checksums are doable without too much of a hit.
Peter.
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