What external capacity tiers and tiering policies are

External capacity tiers provide storage for infrequently accessed data. You can attach an all flash (all SSD) aggregate to an external capacity tier to store infrequently used data. You can use tiering policies to decide whether data should be moved to an external capacity tier.

You can set one of the following tiering policies on a volume:

Snapshot-only
Moves the Snapshot copies of only those volumes that are currently not being referenced by the active file system. Snapshot-only policy is the default tiering policy.
None
Prevents the data on the volume from being moved to an external capacity tier.
Backup
Moves the newly transferred data of a data protection (DP) volume to the external capacity tier.
Auto
Moves the inactive (cold) data and the Snapshot copies from the active file system to the external capacity tier.