Data Read, Write, and Recall

Once offloaded to the storage tier, data is considered to be cold on the storage tier, but the data can still be accessed (read, written, and recalled).

Read of Tiered Data

When the standard volume data is outside of the fabric storage, and in the cloud (cold tiering) , Data Fabric processes the request to read standard volume data and mirror volume data.

Data Reads on Tiering-enabled Standard Volume

When a client attempts to read, the read request is first sent to the volume on the fabric and if the data exists in the volume on the fabric, the data is returned from the volume. On the other hand, if the data was offloaded to a storage tier, Data Fabric recalls the data from the cold-tier to process the read request.

Data Reads on Tiering-enabled Mirror Volume

When a client attempts to read, the read request is first sent to the volume on the Data Fabric cluster and if the data exists in the volume on the cluster, the data is returned from the volume. On the other hand, if the data was offloaded, Data Fabric recalls or fetches a copy of the data (from the tier) into an associated cache-volume, from where data is returned to the client.

Write on Tiered Data

When writes happen, if the write is:

  • An append, new data is offloaded when the data meets the criteria in the rule (associated with the volume) for offload.
  • A change to existing data (overwrite), the data is recalled to the Data Fabric file system to allow the write to succeed and then offloaded when the data meets the criteria in the rule (associated with the volume) for offload.
NOTE
If cold data is accessed (read/written) frequently, I/O to that file may suffer large latencies. In such scenarios, recall the whole volume or the corresponding files.

Recall of Tiered Data

Offloaded data is automatically recalled when a client performs a read or overwrite on the data in the cold-tier, or when a client performs an overwrite on the data in the warm-tier. Data Fabric fetches a copy of the data to allow the operations to succeed.