VAST's asynchronous replication technology enables you to set up a recurring data replication schedule for disaster recovery or long-term data retention, in which you replicate data from a primary cluster to another cluster or to multiple destination clusters. Destination clusters can reside at remote locations, anywhere in the world.
VAST async replication provides capability to fail over, fail back, suspend and resume, and break replication relationships between clusters, as needed to recover data after a failure, corruption or for any other reason.
With VAST asynchronous replication, you can:
Maintain a backup copy of your data for regulatory purposes.
Recover data in the event of disaster.
Fail over to a remote cluster in a disaster event in order to continue operations.
Fail back to the source cluster following failover, if the source cluster is healthy.
In asynchronous replication, the state of data on a path is captured on the source peer by snapshots at points in time. At each point in time, the data on the path that has changed since the last point in time is captured in a snapshot and transferred to destination peers.
Clusters in an async replication configuration where snapshots are copied from cluster to cluster are called replication peers. The configuration of a replication peer is done on one cluster and then mirrored to the other cluster.
During replication, each peer has a role which reflects its part in replication. The role of the peer on which the snapshots are created is called source. The role of a peer to which snapshots are transferred by the source peer is called destination.
The roles of a peer can change as follows:
A cluster acting as a destination peer can become the replication source in a failover. Failover can be graceful, where the original source peer is reachable throughout the process, or ungraceful, if the source peer became unreachable and a decision is made to force a failover from a destination peer, which becomes the source. Any other destination peers (see group replication below) continue to be destination peers. In graceful failover, the former source peer also becomes a destination peer. During graceful failover, both the former source peer and the new source peer are read-only while data is transferred from old source to new source. When failover is complete, the new source peer becomes writeable.
A destination peer can break replication. This means that replication to that destination peer is ceased, although the source peer may continue to replicate to other destination peers. The role of that destination peer becomes standalone and the data that was replicated to that peer becomes writable.
On a destination peer, a read-only replica of the data is stored at a chosen path. This replica is based on the most recent snapshot that was transferred from the source peer. Snapshots that were transferred from the source peer and did not yet expire are stored in the .snapshots directory under the same path.
A protection policy specifies the replication peer and defines the chosen schedule for replication from the source peer to the destination peer. When you create a protection policy for async replication, the policy itself is mirrored to the other peer.
A protected path specifies a local path that it protects through snapshots and/or replication. It can specify one or more replication streams, each of which specifies a protection policy and a remote path on the remote peer specified by the protection policy. The local path is the data path on the source peer that is captured in the snapshots. The remote path in each replication stream is a path on a destination peer to which the data is replicated. The remote path is kept updated to the most recently transferred snapshot and the data is stored as read-only.
The transfer of a snapshot to the destination peer is called the creation of a restore point.
Data can be replicated from a VAST Cluster to multiple other VAST Clusters and from multiple VAST Clusters to one VAST Cluster. Maximum limits of replication peers, protected paths and protection policies apply per release. See VAST Cluster Scale Guidelines for limits.
In one to one replication where one of the two peer clusters is running an earlier version of VAST Cluster (prior to 4.7), it is possible to configure more than one protected path on the same path. In this case, each protected path can have only one replication stream. Two protected paths must not replicate the path to the same replication peer. Also, failover is not allowed when there is more than one protected path on the same path.
When the two peer clusters are both running VAST Cluster 4.7 only one protected path per local path is supported, while the protected path can have multiple replication streams, each replicating to a different peer.
You can configure a group of replication peers in a relationship where one peer is the replication source and it replicates data on a given path to all of the other peers in the group. This configuration enables failover to one of the destination peers. Replication is automatically resumed, now from the new source to the old source, as soon as the new source has all the data. It is also automatically resumed to the rest of the peers once they are in sync with the new source.
Group replication is supported only from VAST Cluster 4.7. Clusters running earlier versions of VAST Cluster cannot be group members.