The backup tiering policy is specifically designed for Data Protection (DP) volumes, which include SnapMirror and SnapVault destinations. When this policy is applied to a destination volume, ONTAP immediately tiers all data blocks transferred from the source to the external capacity tier. This behavior is ideal for secondary backup or disaster recovery data, as it frees up space on the high-performance SSD aggregate almost instantly, aligning perfectly with the goal of storing destination SnapMirror data on a capacity tier.

A. auto: This policy tiers cold data from both the active file system and snapshots based on inactivity, which is not optimized for the immediate tiering of newly transferred DP data.

B. snapshot-only: This policy only tiers cold data blocks that are part of Snapshot copies and not in the active file system. It is not the most efficient policy for a DP volume.

C. none: This policy explicitly disables tiering for the volume, ensuring all data remains on the performance tier, which is the opposite of the stated requirement.

1. NetApp ONTAP Documentation, "Data protection on FabricPool aggregates": In the section "Tiering policies for data protection volumes," it states, "You can use the backup tiering policy on a data protection volume to move all the data blocks to the capacity tier. The backup policy is intended for data protection volumes that are SnapMirror destinations."

2. NetApp Technical Report TR-4598, "FabricPool Best Practices": In the "Tiering Policies" section, under the subsection "Backup Policy," it specifies, "The backup policy is designed for use with SnapVault and SnapMirror destination volumes. When the backup policy is used, data is tiered to the capacity tier as soon as it is transferred to the destination volume."

3. NetApp ONTAP Command Reference, volume modify: The description for the -tiering-policy parameter lists backup as an option and its documentation clarifies its use for "moving all blocks of a data protection volume to the capacity tier."