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Understanding RAID disk types
Data ONTAP classifies disks as one of four types for RAID: data, hot spare, parity, or dParity. The RAID disk type is determined by how RAID is using a disk; it is different from the Data ONTAP disk type.
Data disk
Holds data stored on behalf of clients within RAID groups (and any data generated about the state of the storage system as a result of a malfunction).
Spare disk
Does not hold usable data, but is available to be added to a RAID group in an aggregate. Any functioning disk that is not assigned to an aggregate but is assigned to a system functions as a hot spare disk.
Parity disk
Stores data reconstruction information (XOR parity) for the other disks in that RAID group.
dParity disk
Stores double-parity information for the other disks in that RAID group, if RAID-DP is enabled.

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