Although not directly related to high availability, the reduction in I/O operations per second (IOPS) introduced in Exchange 2013 influences the levels of availability provided by an Exchange deployment.

Passive database copies in Exchange 2010 had a checkpoint depth of only 5 MB to ensure a fast failover (a log of checkpoint depth is used to guarantee that log/database cache changes are written faster to the database). Additionally, passive copies performed pre-reading of data aggressively to keep up with the 5 MB checkpoint depth. This caused the IOPS of passive database copies to be the same as the IOPS of active database copies. On the other hand, Exchange 2013 is capable of providing a fast failover, though it uses a high checkpoint depth of 100 MB on passive database copies. As such, Microsoft was able to de-tune passive database copies such that they are not so aggressive. As a result of both these changes, the IOPS of passive database copies...