During normal companion mode, the performance of the system procedures that update user information (sp_addlogin, sp_addrole, and so on) and commands like create database is slightly degraded because the primary companion must perform the command locally and then synchronize this information with the secondary companion. For example, if you add user “joe” to the primary companion, both the primary companion and the secondary companion must update syslogins to include this new user.
Performance after failover depends on the configuration of the secondary companion. If the secondary server is configured similarly to the primary companion’s server, the performance should be similar before and after failover. However, if the secondary server is not as robust (for example, has less memory or fewer CPUs) as the primary server, then the performance after failover will be degraded. The performance of the secondary companion can also be degraded after failover because it is now running both the primary companion and any applications it was running before the failover.
