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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