IMPORTANT: Check the
latest release notes before you attempt to use the Peer Persistence feature.
Automatic Switchover (ASO) is an optional, but highly recommended, feature
that can be used with synchronous replication to enable automatic failure recovery. When
ASO is used in conjunction with synchronous replication, the feature is known as HPE
Peer Persistence.
The HPE Peer Persistence feature enables synchronous replication with ASO,
which allows your arrays to recover automatically and non-disruptively from storage
based failures.
NOTE: The HPE Peer Persistence feature is
designed to enable automatic recovery failure in the event of storage failures. The
feature will not prevent site-to-site failures that result from host level
failures.
ASO currently works on array groups that consist of two arrays. When ASO
is enabled and a switchover occurs, the partner that serves I/O for a volume collection
is switched, which non-disruptively reverses the direction of the synchronous
replication.
ASO facilitates automatic failure recovery through the use of a Witness
daemon that can be run on an independent host (or in a separate VM) that can communicate
with the group leader and the backup group leader.
NOTE: The Witness does not need to
be on the same subnet as the array group, but its IP address must be routable from
the array group’s management network. The Witness can be installed in a different
data center or even in a cloud environment as long as the round-trip time (RTT)
between the Witness and the two arrays is 250 milliseconds or less. Multiple methods
exist to deploy the Peer Persistence Witness. If the Witness is installed in a
different data center or cloud environment and HPE Storage Support is needed to
resolve an issue with the Witness, consider that if HPE Storage Support cannot
access the data center, cloud environment, or infrastructure, troubleshooting may be
limited.
When the Witness detects that an array is unavailable, the ASO process
performs a handover of affected synchronous replication volume collections and
seamlessly maintains the availability of group services and of synchronously replicated
volumes.
To enable ASO, you must perform one of the following procedures:
- Install and configure the Witness software on a CentOS V7.9.x.
client.
- Run the Witness in a separate VMware based Virtual Machine.
After the Witness is configured, you can then use the array OS GUI or CLI to set
up the Witness and enable Automatic Switchover between the arrays in the group.
NOTE: The ASO check box is selected
by default; however, ASO is not actually enabled unless the Witness is configured.
For example, you might go to in the array OS GUI and see that Enable is checked for Automatic Switchover, but the fields for the
Witness are blank. In this case, ASO is not enabled. You must both configure the
Witness and check the Enable box for ASO to be
configured.
Tip: You can use the following group command to enable or disable ASO from the
CLI.
group --edit --auto_switchover_enabled {yes|no}
For information about enabling, deploying, and testing the HPE Peer
Persistence feature, including possible ASO failure scenarios, refer to HPE Peer Persistence Deployment
Considerations in the HPE InfoSight documentation portal.