Comparison of disk protection options

You should be aware of these considerations when selecting disk protection options:

When using RAID 5 device parity protection, the system continues to run after a single-disk failure. When using RAID 6 device parity protection, the system continues to run after a two-disk failure. With mirrored protection, the system might continue to run after the failure of a disk-related component, such as an IOA or an IOP.

RAID 5 device parity protection requires the capacity of one disk unit that is dedicated to storing parity data in a parity set. RAID 6 device parity protection requires the capacity of two disk units that are dedicated to storing parity data in a parity set. A system with mirrored protection requires twice as much disk capacity as the same system without mirrored protection because all information is stored twice. Mirrored protection might also require more buses, IOPs, and disk IOA, depending on the level of protection that you want. Therefore, mirrored protection is typically more expensive than device parity protection.

Typically, neither device parity protection nor mirrored protection has a noticeable effect on system performance. In some cases, mirrored protection actually improves system performance. The time required to restore data to disk units that are protected by device parity protection is longer than the time required to restore to the same disk devices that do not have device parity protection activated. This is because the parity data must be calculated and written.

This table provides an overview of the availability tools that can be used on the server to protect against different types of failure.
What type of availability is needed? Device parity protection Mirrored protection Basic disk pools Independent disk pool
Protect from data loss due to disk-related hardware failure Yes Yes See note 2 See note 2
Maintain availability Yes Yes No Yes4
Help with disk unit recovery Yes Yes Yes2 Yes2
Maintain availability when input/output adapter (IOA) fails No Yes1 No No5
Maintain availability when disk I/O processor fails No Yes1 No No5
Maintain availability when system bus fails No Yes1 No No5
Site disaster protection No Yes3 No No5
Ability to switch data between systems No No No Yes

Notes:

  1. Depends on hardware used, configuration, and level of mirrored protection.
  2. Configuring disk pools can limit the loss of data and the recovery to a single disk pool.
  3. For site disaster protection, remote mirroring is required.
  4. In a clustered environment, an independent disk pool can help maintain availability.
  5. When using geographic mirroring, independent disk pools can provide site disaster protection.
Parent topic: Plan for disk protection