>>> As others said, RAID6 is RAID5 + a hot spare.
>>
>> No. RAID6 is NOT RAID5 plus a hot spare.
>
> The original phrase was that RAID 6 was like RAID 5 with a hot spare
> ALREADY BUILT IN.
Built-in, or not - it is neither. It is more than that, actually. RAID
6 is like RAID 5 in that it uses parity for redundancy and pays a
write cost for maintaining those parity blocks, but will maintain data
integrity in the face of 2 simultaneous drive failures.
In terms of storage cost, it IS like paying for RAID5 + a hot spare,
but the protection is better.
A RAID 5 with a hot spare built in could not survive 2 simultaneous
drive failures.