In Exchange 2007 and 2010, Continuous Replication operates by shipping copies of the logs created by the active database copy to the passive database copies. With Exchange 2010 SP1, this is known as Continuous Replication - File Mode as the log file is only copied once it is full (1MB). But SP1 introduces a new form of continuous replication known as Continuous Replication - Block Mode. In block mode, when an update is written to the active database log file it is immediately copied to the passive mailbox copies, thus reducing the latency between the time a change is made on the active copy and the time that same change is replicated to a passive copy. This way, if a failure occurs on the active copy, the passive copies will have been updated with most or all of the latest updates.
However, Block Mode is only active when continuous replication is up-to-date in file mode. The Log Copier component monitors the copy and replay queue lengths of databases as transaction logs are generated and takes care of transitioning into and out of block mode automatically.
To determine if continuous replication is operating in block mode or file mode, use the following cmdlet:
Get-Counter -ComputerName <> -Counter “\MSExchange Replication(*)\Continuous replication - block mode Active”
The output will be something similar to:
04/09/2012 11:39:46 \\MBX1\\msexchange replication(mdb32)\continuous replication - block mode active : 1
\\ MBX1\\msexchange replication(mdb25)\continuous replication - block mode active : 1
\\ MBX1\\msexchange replication(mdb24)\continuous replication - block mode active : 1
Here, the “1” means that block mode is active while a “0” means it is not. However, note that your active databases will always show “0”, we are just interested in the passive copies!