On Sat, 2009-11-07 at 17:41 -0500, Dennis Clarke wrote:
> Does the dedupe functionality happen at the file level or a lower block
> level?
it occurs at the block allocation level.
> I am writing a large number of files that have the fol structure :
>
> ------ file begins
> 1024 lines of random ASCII chars 64 chars long
> some tilde chars .. about 1000 of then
> some text ( english ) for 2K
> more text ( english ) for 700 bytes or so
> ------------------
ZFS's default block size is 128K and is controlled by the "recordsize"
filesystem property. Unless you changed "recordsize", each of the files
above would be a single block distinct from the others.
you may or may not get better dedup ratios with a smaller recordsize
depending on how the common parts of the file line up with block
boundaries.
the cost of additional indirect blocks might overwhelm the savings from
deduping a small common piece of the file.
- Bill
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