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Cluster : Storage > Disks : Understanding disks : How drive checksum types affect aggregate and spare management
How drive checksum types affect aggregate and spare management
There are two checksum types available for drives 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 for data access speed, and reserves the smallest amount of capacity for the checksum for drives with 520-byte sectors. AZCS provides enhanced storage utilization and capacity for drives with 512-byte sectors. You cannot change the checksum type of a drive.
To determine the checksum type of a specific drive model, see the Hardware Universe.
Aggregates have a checksum type, which is determined by the checksum type of the drives or array LUNs that compose the aggregate. The following configuration rules apply to aggregates, drives, and checksums:
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Checksum types cannot be combined within RAID groups.
This means that you must consider checksum type when you provide hot spare drives.
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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.
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An aggregate can have RAID groups of both checksum types.
These aggregates have a checksum type of mixed.
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Drives of a different checksum type cannot be used to replace a failed drive.
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You cannot change the checksum type of a drive.

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