The concept of having a high availability group is to ensure that, in the event of a hardware or software failure of your primary server, service to your data is disrupted as little as possible. The failover process ensures that a standby server in the group assumes the role of primary server, and continues to provide access to your data.
The failover process can occur automatically or manually. Manual failover is only required when your group has fewer than three active servers in the group (that is, one primary server and two standby servers).
When automatic failover occurs, the next standby server (as determined by the order in which the servers are listed in the ES_HA_VSAM environment variable) is promoted to be primary server. At the point of reconnection, a 9/125 error is produced, and the new primary server rolls back any in-flight transactions.
As part of the recovery process, the primary server that failed is removed from the iFileshare group, and can only be re-added to the group when the group itself is restarted. This is also true if a standby server fails. If a server's removal leaves the group without a minimum number of servers, file replication will still occur within the group, but the automatic failover process is unavailable until the group is restarted with at least a minimum number of servers.
To ensure your client application can still continue processing when the recovery process completes, you must configure your Fileshare client to automatically reconnect once a connection has been lost; this functionality is only available if you have the following lines to the Fileshare client configuration file (fhredir.cfg):
/um /ra <number-of-attempts> /rd <delay-between-attempts>
If the new primary server is on a remote machine, you must also have configured your mf-client.dat configuration file to locate iFileshare on the new machine; see Configuring Remote Servers in a High Availability Group.