The protection service ensures the stability of the repository by maintaining a specified level of data redundancy, called the data protection level (DPL), for each object in the repository throughout the entire object lifecycle. The DPL for an object is the number of copies of the object data that HCP must maintain.
Each namespace has a service plan that defines both a storage tiering strategy and a data protection strategy for the objects in that namespace. For all objects in a given namespace, the storage tiering strategy defines one or more types of storage as tiers. The data protection strategy specifies the DPL that’s applied to the objects that are stored on each tier.
At any given point in the lifecycle of an object, the data protection strategy specifies the number of copies of the object that must exist in the HCP repository and the storage tier on which each copy must be stored.
Because HCP initially stores all object data and metadata on primary running storage, the service plan for a namespace must always define primary running storage as the initial storage tier, called the ingest tier, and must specify both the data protection level (DPL) and the metadata protection level (MPL) for the ingest tier.
For each object in a given namespace, the ingest tier DPL is the number of copies of the object data that HCP must maintain on primary running storage, from the time when the object is first stored in the repository until the time when the object data is moved onto one or more other storage tiers (if multiple storage tiers are defined for the namespace). The ingest tier MPL is the number of copies of the object metadata that HCP must maintain on primary running storage for as long as the object exists in the repository.
For namespaces on RAIN and VM systems, the default ingest tier DPL is two and the default ingest tier MPL is also two. For namespaces on RAIN and VM systems, the default ingest tier DPL is one and the default ingest tier MPL is also one. At any time, you can modify the service plan for a namespace to set the ingest tier DPL and MPL for that namespace.
For any given namespace, you can assign a service plan which will give the namespace a DPL setting of one (supported on SAIN and VM systems only), two, three, or four. You can also set the ingest tier MPL to one, two, three, or four. However, the ingest tier MPL for a namespace must be equal to the ingest tier DPL for that namespace.
HCP uses the protection service to maintain the correct number of copies of each object in the HCP repository. When the number of existing copies of an object goes below the number of object copies specified in the applicable service plan (for example, because of a logical volume failure), the protection service automatically creates a new copy of that object in another location. When the number of existing copies of an object goes above the number of object copies specified in the applicable service plan, the protection service automatically deletes all unnecessary copies of that object.
The protection service runs according to the active service schedule and in response to certain events. For information on service schedules, see Scheduling services. For information on the events that cause the protection service to run, see Protection service triggers.
© 2016 Hitachi Data Systems Corporation. All rights reserved.