Jeffrey J. Kosowsky wrote at about 15:41:26 -0500 on Thursday, February 17, 
2011:
 > I have been running my BackupPC_digestVerify.pl program to check the
 > rsync digests in my pool.
 > 
 > Looking through the 1/x/x/ tree, I found 3 new bad digests out of
 > about 36000 when using the default blocksize of 2048.
 > 
 > It turns out that those 3 digests have a blocksize !=2048 -- and
 > indeed the digests do verify if you use that blocksize.
 > These files have block size 2327 and 9906 (twice).
 > Note the file sizes are 99MB, 11MB, and 16MB.
 > 
 > This seems *weird* and *wrong* since I thought the blocksize was fixed
 > to 2048 according to the (default) parameters passed to rsync in the
 > config.pl file. Specifically,
 >       '--block-size=2048',
 > 
 > Any idea why rsync may be ignoring this and using a larger blocksize
 > for these files?

OK this is weird... the block size used is the *uncompressed* file
size divided by 10,000 (rounded to integer). 

This too is weird since the normal rsync algorithm uses the rounded
sqrt of the (uncompressed) file length for the blocksize (as long as
it is >700 and < MAX_BLOCK_SIZE which I think may be 16,384).

So what is going on here and why is rsync neither using the
--block-size=2048 value nor the heuristic sqrt(filesize) number?

[Note my numbers in my original post were wrong in that the actual
blocksize  wasn't 9906 twice but 9906 and 4081]

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