On Oct 2, 2009, at 3:05 PM, Ray Clark wrote:
Re: relling's Oct 2, 2009 3:26 Post:
(1) Is this list everything?
AFAIK
(2) Is this the same for U4?
Yes. This hasn't changed in a very long time.
(3) If I change the zpool checksum property on creation as you
indicated in your Oct 1, 12:51 post (evidently very recent versions
only), does this change the checksums used for this list? Why would
not the strongest checksum be used for the most fundamental data
rather than fool around, allowing the user to compromise only when
the tradeoff pays back on the 99% bulk of the data?
Performance. Many people value performance over dependability.
Re: "The big question, that is currently unanswered, is do we see
single bit faults in disk-based storage systems?"
I don't think this is the question. I believe the implication of
schlie's post is not that single bit faults will get through, but
that the current fletcher2 is equivalent to a single bit checksum.
You could have 1,000 bits in error, or 4095, and still have a 50-50
chance of detecting it. A single bit error would be certain to be
detected (I think) even with the current code.
I don't believe schlie posted the number of fletcher2 collisions for the
symbol size used by ZFS. I do not believe it will be anywhere near
50% collisions.
-- richard
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