You can treat whatever hash function as an idealized one, but actual hash functions aren't. There may well be as-yet-undiscovered input bit pattern ranges where there's a large density of collisions in some hash function, and indeed, since our hash functions aren't ideal, there must be. We just don't know where these potential collisions are -- for cryptographically secure hash functions that's enough (plus 2nd pre-image and 1st pre-image resistance, but allow me to handwave), but for dedup? *shudder*.
Now, for some content types collisions may not be a problem at all. Think of security camera recordings: collisions will show up as bad frames in a video stream that no one is ever going to look at, and if they should need it, well, too bad. And for other content types collisions can be horrible. Us ZFS lovers love to talk about how silent bit rot means you may never know about serious corruption in other filesystems until it's too late. Now, if you disable verification in dedup, what do you get? The same situation as other filesystems are in relative to bit rot, only with different likelihoods. Disabling verification is something to do after careful deliberation, not something to do by default. Nico -- _______________________________________________ zfs-discuss mailing list firstname.lastname@example.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss