I was under the impression that the hash (or checksum) used for data
integrity is the same as the one used for deduplication,
but now I see that they are different.

On Wed, Jul 11, 2012 at 10:23 AM, Sašo Kiselkov <skiselkov...@gmail.com>wrote:

> On 07/11/2012 09:58 AM, Ferenc-Levente Juhos wrote:
> > Hello all,
> >
> > what about the fletcher2 and fletcher4 algorithms? According to the zfs
> man
> > page on oracle, fletcher4 is the current default.
> > Shouldn't the fletcher algorithms be much faster then any of the SHA
> > algorithms?
> > On Wed, Jul 11, 2012 at 9:19 AM, Sašo Kiselkov <skiselkov...@gmail.com
> >wrote:
> Fletcher is a checksum, not a hash. It can and often will produce
> collisions, so you need to set your dedup to verify (do a bit-by-bit
> comparison prior to deduplication) which can result in significant write
> amplification (every write is turned into a read and potentially another
> write in case verify finds the blocks are different). With hashes, you
> can leave verify off, since hashes are extremely unlikely (~10^-77) to
> produce collisions.
> --
> Saso
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