CORRECTION: As fletcher4 actually sums 32bit (not 64bit) data using 64bit accumulators, the first two checksum terms (a and b) will not overflow for data block sizes as large as 128KB, and therefore should be considered at least as strong as that expected of a 32/64bit Fletcher checksum (although the remaining terms (c and d) may overflow); and thereby have a worst case hamming distance of at least 3 for zfs's maximum 128KB block size; which is a good thing. (sorry for my earlier miss-diagnosis)
fletcher2 (zfs's default) however remains arguably flawed, however may be easily strengthened by correspondingly being restricted to summing 32bit data using 64bit accumulators, or possibly alternatively summing 64bit data using 128bit accumulators if it's viewed reasonably supportable by target architectures/compilers likely to host zfs. -- This messages posted from opensolaris.org
