Content protection: erasure coding

Following ingest, if an ILM rule includes instructions to make erasure coded copies of object data, the applicable erasure coding scheme breaks object data into data and parity fragments and distributes these fragments across the configured storage pool's Storage Nodes.

Data flow

The Storage Nodes CMS service controls erasure coding and ensures that the correct Erasure Coding profile is applied to object data.

diagram showing process described in surrounding text

The CMS service queries the ADC service to determine which DDS service can best perform the erasure coding operation. Once determined, the CMS service sends an "initiate" request to that service.
The DDS service instructs an LDR to erasure code the object data.
The source LDR service sends a copy to the LDR service selected for erasure coding.
Once broken into the appropriate number of parity and data fragments, the LDR service distributes these fragments across the Storage Nodes (LDR services) that make up the Erasure Coding profile’s storage pool.
The LDR service notifies the CMS service, confirming that object data is successfully distributed.
The CMS service updates the DDS service with object location metadata.

Erasure coding related attributes

The table shows the primary attributes used to track an erasure coded object:

Component	Attribute changes
CMS > Content	ILM Evaluations (ILev): LM Evaluations (ILev): The total number of ILM evaluations increases by one when the object is first evaluated and again when an erasure coded copy is made.
LDR > Storage	Total Usable Space (STAS): The total amount of storage space that is currently available for the storage of object data decreases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node. Total Usable Space (Percent) (SAVP): The total amount of available storage (displayed as a percentage) decreases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node. Total Persistent Data (SPSD): The estimate of the size of the persistently stored data increases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node. Total 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 erasure coded fragment (data or parity) stored to this Storage Node.
LDR > Erasure Coding	Writes - Successful (ECWC): The total number of erasure coded objects increases by one.

Component

Attribute changes

CMS > Content

ILM Evaluations (ILev): LM Evaluations (ILev): The total number of ILM evaluations increases by one when the object is first evaluated and again when an erasure coded copy is made.

LDR > Storage

Total Usable Space (STAS): The total amount of storage space that is currently available for the storage of object data decreases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node.

Total Usable Space (Percent) (SAVP): The total amount of available storage (displayed as a percentage) decreases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node.

Total Persistent Data (SPSD): The estimate of the size of the persistently stored data increases by an amount roughly equivalent to the size of the erasure coded fragment (data or parity) stored to this Storage Node.

Total 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 erasure coded fragment (data or parity) stored to this Storage Node.

LDR > Erasure Coding

Writes - Successful (ECWC): The total number of erasure coded objects increases by one.