On Wed, July 11, 2012 04:50, Ferenc-Levente Juhos wrote:
> Actually although as you pointed out that the chances to have an sha256
> collision is minimal, but still it can happen, that would mean
> that the dedup algorithm discards a block that he thinks is a duplicate.
> Probably it's anyway better to do a byte to byte comparison
> if the hashes match to be sure that the blocks are really identical.
>
> The funny thing here is that ZFS tries to solve all sorts of data
> integrity
> issues with checksumming and healing, etc.,
> and on the other hand a hash collision in the dedup algorithm can cause
> loss of data if wrongly configured.
>
> Anyway thanks that you have brought up the subject, now I know if I will
> enable the dedup feature I must set it to sha256,verify.
There was a long-ish thread on the topic last year
("(Fletcher+Verification) versus (Sha256+No Verification) "):
http://mail.opensolaris.org/pipermail/zfs-discuss/2011-January/thread.html#46864
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