Content protection: replication

Following ingest, if an ILM rule’s Content Placement instructions are configured to make replicated copies of object data, copies are made and stored to disk through the LDR services of Storage Nodes that make up the configured storage pool.

Data flow

The CMS service controls replication and ensures that the correct number of copies are stored in the correct locations and for the correct amount of time.
diagram showing the process described in surrounding text
  1. The CMS service queries the ADC service to determine the best destination LDR service within the storage pool as defined by the ILM policy, and sends that LDR service a command to initiate replication.
  2. The destination LDR service queries the ADC service for the best source location and sends a replication request to the source LDR service.
  3. The source LDR service sends a copy to the destination LDR service.
  4. The destination LDR service notifies the CMS service that the object data has been stored.
  5. The CMS service updates the DDS service with object location metadata.

Replication related attributes

The table shows the primary attributes used to track a replicated object:

Component Attribute changes
CMS > Content ILM Evaluations (ILev): The total number of ILM evaluations that have been performed to date increases when the object is evaluated after ingest and again when a copy of object data is made.
Note: The number of evaluations is dependent on the StorageGRID Webscale system’s ILM rules.

Total Transfers (DCdT): The total number of object transfers performed by the CMS service since system start-up increases by one each time a copy of object data is made.

LDR > Storage

Total Usable Space (STAS): The total amount of object storage space that is currently available to be used to store objects decreases by an amount roughly equivalent to the object’s size.

Total Usable Space (Percent) (SAVP): The total amount of object storage space (displayed as a percentage) that is currently available to be used to store objects decreases by an amount roughly equivalent to the object’s size.

Total Persistent Data (Percent) (SPSD): The estimate of the size of the persistently stored data increases by an amount roughly equivalent to the object’s size.

Total Persistent Data (Percent) (SPDP): The percentage of the total storage space used by persistent data on each destination LDR service increases by an amount roughly equivalent to the size of the replicated object.

Objects Retrieved (ORET): The number of persistent objects retrieved from the source LDR service increases by one.

Objects Committed (OCOM): The number of persistent objects stored on each destination LDR service increases by one each time a replicated copy is made.

destination LDR > Replication Inbound Replications Completed (RIRC): The total number of objects replicated to the destination LDR service increases by one.
source LDR > Replication Outbound Replications Completed (RORC): The total number of objects replicated from the source LDR service increases by one.