What is "Raid 5 + Spare" (excerpt from User Manual, Sect 4.17.2, P.54):

RAID5+Spare: RAID 5+Spare is a RAID 5 array in which one disk is used as spare to rebuild the system as soon as a disk fails (Fig. 79). At least four disks are required. If one physical disk fails, the data remains available because it is read from the parity blocks. Data from a failed disk is rebuilt onto the hot spare disk. When a failed disk is replaced, the replacement becomes the new hot spare. No data is lost in the case of a single disk failure, but if a second disk fails before the system can rebuild data to the hot spare, all data in the array will be lost.

What is "Raid 6" (excerpt from User Manual, Sect 4.17.2, P.54):

RAID6: In RAID 6, data is striped across all disks (minimum of four) and a two parity blocks for each data block (p and q in Fig. 80) is written on the same stripe. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. This Raid mode can support up to two disk failures with no data loss. RAID 6 provides for faster rebuilding of data from a failed disk.

Both "Raid 5 + spare" and "Raid 6" are SO similar ... I can't tell the difference.

When would "Raid 5 + Spare" be optimal?

And when would "Raid 6" be optimal"?

The manual dumbs down the different raid with 5 star ratings. "Raid 5 + Spare" only gets 4 stars but "Raid 6" gets 5 stars. If I were to blindly trust the manual I would conclude that "Raid 6" is always better. Is "Raid 6" always better?