Considerations for tiering objects from primary storage to S Series or extended storage

When moving an object to a storage tier that includes only S Series or extended storage pools, the Storage Tiering service moves only the object data onto the S Series or extended storage that’s used for the new tier.

Note: For the purpose of storage tiering, HCP treats parts of multipart objects, chunks for erasure-coded objects, and chunks for erasure-coded parts of multipart objects as individual objects.

HCP keeps all metadata, including custom metadata, for an object on primary running storage. The system metadata for an object points to each specific NFS volume and each specific S Series or extended storage bucket or container that’s used to store the data for that object. Primary storage keeps metadata even if S Series storage is used as an ingest tier alternative to running storage instead of as a storage tier.

All objects added to a namespace are first written to the ingest tier defined in their namespace service plan. However, HCP can read the data for an object directly from any storage component the object may later be tiered too.

The service plan for a given namespace defines one or more storage tiers for that namespace and specifies a separate DPL setting for each tier, including the ingest tier. When an object is moved from one storage tier to another, all copies of the object data are removed from the previous tier, and the object is then stored only on the new tier. The DPL for the new tier is the total number of copies of the object data that must be stored on that tier. The DPL is also the total number of copies of the object data that must be stored in the HCP repository. (For a metadata-only tier, the DPL is zero.)

When the Storage Tiering service moves an object in a given namespace from a storage tier that includes only ingest tier storage pools to a tier that includes only extended storage pools, the Storage Tiering service removes all existing copies of the data for that object from the ingest tier storage and stores the specified number of copies of the object data only on the extended storage that’s represented by the pools that are configured for the new storage tier.

The Storage Tiering service moves all copies of the data for an object to S Series or extended storage only if all of these are true:

The cryptographic hash algorithm for the object has been stored in both the primary and secondary metadata for the object.

The object is not still open for write. For more information about open objects, see Using a Namespace or Using the Default Namespace.

The object is not a part of an in-progress multipart upload.

If the namespace containing the object is being replicated and the target tier is extended storage, the object has already been replicated. The Storage Tiering service can move objects to S Series storage before the objects are replicated.

The namespace containing the object has a service plan that defines a storage tier that includes only S Series or extended storage pools, and the object meets the criteria for being moved to that tier.

An HCP system can have a full copy of the data for an object that is subject to erasure coding but that has not yet been erasure coded. The Storage Tiering service can tier the data for such an object to S Series or spindown storage but not to extended storage.

While the data for an object is stored only on S Series or extended storage:

If the object is deleted, the data that’s on S Series or extended storage is also deleted

If the object is an old version that’s pruned, the version data that’s stored on S Series or extended storage is also deleted

If the object is shredded, the data that’s stored on S Series or extended storage is not shredded

For more information about the movement of objects between primary storage and S Series or extended storage, see Storage Tiering service and Working with service plans.

For more information about S Seriess and extended storage, see Storage for HCP systems.

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