NetApp RAID levels
The article is slightly misleading about the RAID levels that NetApp use - to their disfavour.
The original NetApp protection was RAID 4 - all the parity is written to one dedicated disk per RAID set. This wasn't a problem with one disk being "hot" since unlike most RAID 4 or 5 implementations, there is only one write per disk; parity being calculated in memory, not by calculating the parity from reading what has already been written and then rewriting this to the parity disk (standard RAID4) or over the whole RAID set (RAID 5).
What the article claims as RAID 6 (double parity disks) is wrong. NetApp uses their own form of RAID 4 with a second dedicated disk for the "diagonal" parity. Standard RAID6 however spreads both of the parity stripes across the whole set. NetApp use two dedicated disks for their "double" parity and again, the number of read / calculate parity / write operations are drastically reduced as compared to other hardware RAID - all the fancy work is built into the kernel of the operating system.
Not that I work for NetApp you understand, (wouldn't mind though).