A volume consists of disks assembled into one or multiple RAID groups. A RAID group consists of one or more data disks, across which client data is striped and stored, plus one or two parity disks that ensure data recoverability even if as many as two disks within the RAID group fail. The purpose of a RAID group is to provide parity protection of data across its included disks from loss due to single or double disk failure within that group.
Data ONTAP supports two types of RAID protection, which you can assign on a per-volume basis: RAID 4 and RAID DP.
Before Data ONTAP 6.5, RAID 4 was the only RAID protection for Data ONTAP volumes. Within its RAID groups, it allots a single disk for holding parity data, which ensures against data loss due to a single disk failure within a group.
RAID DP provides a higher level of RAID protection for Data ONTAP volumes. Within its RAID groups, it allots two disks for holding parity and double-parity data. Double-parity protection ensures against data loss due to a double disk failure within a group.
For more information on RAID 4 and RAID DP, see Types of RAID protection.
When you create a volume, you can also control the size of a RAID group. Generally, larger RAID groups maximize your data storage space (by providing a greater ratio of data disks to parity disks) and maximize system performance (data striping across a larger number of disks). Smaller RAID groups minimize the risk of multiple disk failure and the performance impact during the subsequent reconstruction. For information on RAID size considerations, see Larger versus smaller RAID groups.
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File: data-or4.htm
Last updated: 11/17/03 16:57:17