Re: Two-disk RAID5?

[John Rowe <rowe@excc.ex.ac.uk>]

> Sorry, I couldn't find a diplomatic way to say you're completely wrong.

We don't necessarily expect a diplomatic way, but a clear and
intelligent one would be helpful. 

In two-disk RAID5 which is it?

  1) The 'parity bit' is the same as the datum.

  2) The parity bit is the complement of the datum.

  3) It doesn't work at a bit-wise level.

Many of us feel that RAID5 looks like:

  parity = data[0];
  for (i=1; i < ndisks; ++i)
      parity ^= data[i];

which implies (1). It could easily be (2) but merely saying "it's not
data, it's parity" doesn't clarify matters a great deal. 

But I'm pleased my question has stirred up such controversy!

John