On Fri, January 7, 2011 01:42, Michael DeMan wrote: > Then - there is the other side of things. The 'black swan' event. At > some point, given percentages on a scenario like the example case above, > one simply has to make the business justification case internally at their > own company about whether to go SHA-256 only or Fletcher+Verification? > Add Murphy's Law to the 'black swan event' and of course the only data > that is lost is that .01% of your data that is the most critical?
The other thing to note is that by default (with de-dupe disabled), ZFS uses Fletcher checksums to prevent data corruption. Add also the fact all other file systems don't have any checksums, and simply rely on the fact that disks have a bit error rate of (at best) 10^-16. Given the above: most people are content enough to trust Fletcher to not have data corruption, but are worried about SHA-256 giving 'data corruption' when it comes de-dupe? The entire rest of the computing world is content to live with 10^-15 (for SAS disks), and yet one wouldn't be prepared to have 10^-30 (or better) for dedupe? I certainly can understand caution, but given the numbers involved, you're more likely to be hit by lighting a few times in a lifetime before a collision occurs for a reasonably sized ZFS pool. :) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
