As a rule of thumb one parity disk (RAID5) can be used with up to four data disks, and then using one parity disk for each group of seven data disks, like in the table:
| Parities | Data disks |
|---|---|
| 1/Single Parity/RAID5 | 2 - 4 |
| 2/Double Parity/RAID6 | 5 - 14 |
| 3/Triple Parity | 15 - 21 |
| 4/Quad Parity | 22 - 28 |
| 5/Penta Parity | 29 - 35 |
| 6/Hexa Parity | 36 - 42 |
NOTE: This table takes into account that more parity levels also help to recover from unsynced array.