How RAID groups work

The purpose of a RAID group is to provide parity protection from data loss across its included disks.

A RAID group consists of one or more data disks, across which client data is striped and stored, plus one or two parity disks. RAID4 uses one parity disk to ensure data recoverability if one disk fails within the RAID group. RAID-DP uses two parity disks to ensure data recoverability even if two disks within the RAID group fail.

• How RAID groups are named
  Within each aggregate, RAID groups are named rg0, rg1, rg2, and so on in order of their creation. You cannot specify the names of RAID groups.
• About RAID group size
  A RAID group has a maximum number of disks that it can contain. This is called its maximum size, or its size. A RAID group can be left partially full, with fewer than its maximum number of disks, but storage system performance is optimized when all RAID groups are full.
• Maximum number of RAID groups
  Data ONTAP supports up to 400 RAID groups per storage system or active/active configuration.
• Maximum and default RAID group sizes
  Maximum and default RAID group sizes vary according to the storage system model, level of RAID group protection provided, and the types of disks used in the RAID group. Generally, you should use the default RAID group sizes.
• Considerations for sizing RAID groups
  Configuring an optimum RAID group size for an aggregate requires a trade-off of factors. You must decide which factor--speed of recovery, assurance against data loss, or maximizing data storage space--is most important for the aggregate that you are configuring.