On Mon, Dec 19, 2016 at 1:24 PM, Dan Kimmel <[email protected]> wrote:

>
> 2. If one big file changes (such as one row in a database table), docker
>> registry will store the whole file in the image (which my hacked registry
>> would be extracting to a normal tree). Whilst I could use zfs dedup, my
>> researches indicate this is pretty memory intensive. I'd prefer a mechanism
>> where I supply ZFS with the paths to two nearly identical files and it
>> dedups the blocks. If this was doable while writing the derived file
>> instead of after writing all the data to disk, that'd be even better.
>>
>
> The solution you're proposing is kind of similar to a feature in ZFS
> called "nop write", where overwriting a block in a file with an exact
> duplicate of the data that's already there will result in no write being
> issued. I don't think you have to do anything to enable this behavior.
>

Nop-write only takes effect when using a checksum algorithm that has an
undetectably low collision rate: sha256, sha512, skein, or edonr.  This
still performs much much better than dedup!

--matt



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