How disk checksum types affect aggregate and spare management

There are two checksum types available for disks used by Data ONTAP: BCS (block) and AZCS (zoned). Understanding how the checksum types differ and how they impact storage management enables you to manage your storage more effectively.

Both checksum types provide the same resiliency capabilities; BCS optimizes data access speed and capacity for disks that use 520 byte sectors. AZCS provides enhanced storage utilization and capacity for disks that use 512 byte sectors (usually SATA disks, which emphasize capacity).

Aggregates have a checksum type, which is determined by the checksum type of the disks that compose the aggregate. The following configuration rules apply to aggregates, disks, and checksums:

• Checksum types cannot be combined within RAID groups.

  This means that you must consider checksum type when you provide hot spare disks.

• When you add storage to an aggregate, if it has a different checksum type than the storage in the RAID group to which it would normally be added, Data ONTAP creates a new RAID group.
• An aggregate can have RAID groups of both checksum types.

  These aggregates have a checksum type of mixed.

• For mirrored aggregates, both plexes must have the same checksum type.
• Disks of a different checksum type cannot be used to replace a failed disk.
• You cannot change the checksum type of a disk.