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13 Dell PS Series Storage: Choosing a Member RAID Policy | TR1020 | v 4.7
If a set is degraded: Data is reconstructed on the new disk and after reconstruction, performance returns to
normal.
2.4 Examples of data protection with different RAID policies
The following table and figures show the results of a 24-disk, PS6210 series array responding to failures in
the same RAID set based on the member RAID policy.
Note: The figures show a logical disk layout when an array is initialized for the first time. The actual physical
layout of disks can change and evolve due to maintenance and administrative actions. Spare disks can
move as they are utilized to replace failed disks and newly added disks become the spares. It is not possible
to determine which physical disks are associated with each RAID set. This information is dynamic and
maintained by the PS Series firmware.
Table 4 lists the RAID set relationship for each RAID policy in a 24-disk PS6210 series array. See Appendix B
for PS65xx series arrays and Appendix C for PS6610 series arrays.
PS Series PS6210 Series array RAID policy and disk set relationships
RAID policy
Spare disks
Disk RAID set
relationship
Best practice
RAID 6
1 Spare Disk
(10+2) (9+2)
Yes
RAID 10
2 Spare Disks
(6+6) (5+5)
No for 6 TB and larger
disks
RAID 50
2 Spare Disks
(5+1 5+1) (4+1 4+1)
For selected
configurations
1
1
RAID 50 is not recommended for arrays with 1 TB or larger disks.
Note: The disk RAID set relationship indicates the number of data disks to parity or mirror disks ([data disk]
+ [parity|mirror disk]).
2.4.1 RAID 6
The following figures show how RAID 6 provides capacity and protection from single or dual disk failures for a
24-disk, PS6210 series array. RAID 6 provides higher availability because each RAID 6 set can survive two
disk failures. This level of RAID is best used with larger physical disk sizes and for data that requires the
highest level of protection and reliability.
In the following figures, the member RAID policy is RAID 6 with spares. There is only one spare in a 24-disk
array with RAID 6. RAID and the spare disk protect the data. The second figure shows the reliability that RAID
6 offers by allowing a second disk failure protection in each RAID set.