HCP System Management Help
To fully understand how certain services work, you need to know how HCP manages metadata. When you add an object, directory, or symbolic link to a namespace:
1.HCP creates primary metadata for it. This metadata consists of information HCP already knows, such as the creation date, and, for objects only, the data size, hash algorithm, and cryptographic hash value generated by that algorithm. It also includes metadata that was either inherited or specified in the write request, such as retention setting, UID, and GID.
2.HCP creates the number of additional copies of the primary metadata required to satisfy the ingest tier metadata protection level (MPL) that’s set for the namespace by its service plan. HCP then distributes all copies of the primary metadata among the HCP storage nodes.
3.For objects:
a.HCP creates the number of copies of the object data required to satisfy the ingest tier data protection level (DPL) that’s set for the namespace by its service plan. HCP then distributes all copies of the object data among the HCP storage nodes.
Each copy of the primary metadata for the object points to all copies of the object data. However, the object data is not necessarily stored on the same node as the primary metadata for the object.
b.HCP stores a copy of the metadata with each copy of the object data. Each copy, called the secondary metadata, lets HCP reconstruct the primary metadata should that become necessary.
The figure below outlines the data and metadata that result from storing an object in a namespace that has a service plan that sets both the ingest tier DPL and the ingest tier MPL to 2.
For more information on metadata, see Using a Namespace or Using the Default Namespace.
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