[CentOS] block level changes at the file system level?

Lists wrote:
> On 07/02/2014 12:57 PM, m.roth at 5-cent.us wrote:
>> I think the buzzword you want is dedup.
> dedup works at the file level. Here we're talking about files that are
> highly similar but not identical. I don't want to rewrite an entire file
> that's 99% identical to the new file form, I just want to write a small
> set of changes. I'd use ZFS to keep track of which blocks change over
> time.
>
> I've been asking around, and it seems this capability doesn't exist
> *anywhere*.

I was under the impression from a few years ago that at least the
then-commercial versions operated at the block level, *not* at the file
level. rsync works at the file level, and dedup is supposed to be fancier.

       mark