RE: [MI400] Reverse of XOR.

[Jim Langston <jlangston@xxxxxxxxxxx>]

Hmm... XOR 1 1 0 would be 0.  XOR 1 1 1 0 would also be 0, no?
XOR would only be a 1 if only one bit was a 1.  Or are the bits XORed pair by 
pair?

1 XOR 1 = 0, 0 XOR 0 = 0.  Still 0.  1 XOR 1 = 0, 0 XOR 1 = 1, 1 XOR 0 = 1.  
Hmm.. maybe you have something there.
0 1 1 1 = 0 XOR 1 = 1, 1 XOR 1 = 0, 0 XOR 1 = 1
1 0 1 1 = 1 XOR 0 = 1, 1 XOR 1 = 0, 0 XOR 1 = 1

I'll have to look into this.

Regards,

Jim Langston

-----Original Message-----
From: Leif Svalgaard [mailto:leif@leif.org]

From: Jim Langston <jlangston@celsinc.com>
My understanding of how RAID 5 works.
Disk5 will set the bit on or off to make the parity even.  It adds up the
bits in the other disks, if they are odd, it will set the bit to 1, if they
are even, it will set it to 0.

===> in other words: the parity is an XOR of the other bits.
This is how parity has always been defined. Now if the ECC
method is used, it is wrong to talk about "parity". "Check bits"
would be a better term. Aren't the a couple of Cs in ECC to
hint at that?  :-)