Hi David,

My current state is that I've got theory worked out and written up -
not just for triple parity, but for more parities as well.  For some
of it, I've got Python code to test and verify the maths.  It turns
out that triple parity can work well - but for quad parity the limit
is 21 data disks (using generators 2, 4, and 8), or up to 33 (using
for example 0x07, 0x35 and 0x8b as generators).  Realistically, I
think triple parity is the limit for practical implementations.

Why is that? An RS code (255,251) should be possible, like
it is a (255,223). What's the limitation?
I'm sure there is even a "RAID-96", which is (96,64).

My wild guess would be that the generators must be chosen
in some way.

Have you had a look at the "par2" code? That seems to be
capable of doing a parametric RS, even if in 16bit words.

bye,

-- 

piergiorgio