> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Sašo Kiselkov
> On 07/11/2012 11:53 AM, Tomas Forsman wrote:
> > On 11 July, 2012 - Sa??o Kiselkov sent me these 1,4K bytes:
> >> Oh jeez, I can't remember how many times this flame war has been going
> >> on on this list. Here's the gist: SHA-256 (or any good hash) produces a
> >> near uniform random distribution of output. Thus, the chances of
> >> a random hash collision are around 2^-256 or around 10^-77. If I asked
> >> you to pick two atoms at random *from the entire observable universe*,
> >> your chances of hitting on the same atom are higher than the chances of
> >> that hash collision. So leave dedup=on with sha256 and move on.
> >
> > So in ZFS, which normally uses 128kB blocks, you can instead store them
> > 100% uniquely into 32 bytes.. A nice 4096x compression rate..
> > decompression is a bit slower though..
> I really mean no disrespect, but this comment is so dumb I could swear
> my IQ dropped by a few tenths of a point just by reading.

Cool it please.  You say "I mean no disrespect" and then say something which
is clearly disrespectful.

Tomas's point is to illustrate that hashing is a many-to-one function.  If
it were possible to rely on the hash to always be unique, then you could use
it as a compression algorithm.  He's pointing out that's insane.  His
comment was not in the slightest bit dumb; if anything, it seems like maybe
somebody (or some people) didn't get his point.

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