Retrieve

Retrieval refers to the process of a client application accessing an object stored by the StorageGRID Webscale system.

Data flow

The Storage Node's LDR service queries the DDS service for the location of the object data and retrieves it from the source LDR service after obtaining the location from the DDS service. Preferentially, retrieval is from disk. When there is no higher grade copy accessible, the retrieval request is directed to the Archive Node.
Retrieve

  1. The LDR service receives a retrieval request from the client application.
  2. The LDR service queries the DDS service for the object data location.
  3. LDR service forwards the retrieval request to the source LDR service.
  4. The source LDR service returns the object data from the queried LDR service and the system returns the object to the client application.

Retrieval related attributes

The table shows the primary attributes used to track the retrieval of an object from the StorageGRID Webscale system:

Component Attribute changes
LDR > S3 Operations - Successful (SSUC): The total number of successful S3 operations increases by one.
LDR > Swift Operations - Successful (WSUC): The total number of successful Swift operations increases by one.
LDR > Storage Objects Retrieved (ORET): The number of replicated objects retrieved from the source LDR service increases by one.
LDR > Erasure Coding EC Reads - Successful (ECRC): The number of erasure-coded objects retreived from the source LDR service increases by one.
ARC > Retrieve Client Requests (ARCR): The total number of requests received from clients for archived object data increases by one with each attempt to retrieve object data from this Archive Node. Retrieval from the Archive Node only occurs if object data is not available on a Storage Node.

Active Retrieves (ARAR): The number of object retrievals in progress increases by one while retrieval is taking place through this Archive Node and then decreases by one once retrieval is complete.