Idle Storage Groups and CCR…


Let’s say that over a period of an hour only a very small number of transactions are generated for a particular CCR enabled storage group.  If those changes add up to less than 1MB’s worth of transactions and are therefore not sufficient to fill up and close the current log file does that mean those transactions are not replicated to the passive database for an hour?

The answer is explained in the following whitepaper:

White Paper: Continuous Replication Deep Dive
http://technet.microsoft.com/en-us/library/cc535020(EXCHG.80).aspx

ESE now forces the active log to close after a period of time.  The time is based upon the LLR (Lost Log Resilience) depth which in Exchange 2007 SP1, with CCR enabled, is set to 10.  (At RTM the LLR depth is different dependent on what AutoDatabaseMountDial is set to.)

The formula to calculate when log roll will occur is:

[15 (minutes) ÷ LLR Depth value] = Frequency of log roll activity (in minutes)

In effect log roll will occur every 90 seconds when insufficient transactions occur to fill the current log.  This means that for a completely idle storage group 960 transaction logs will be generated over a 24 hour period for a CCR enabled storage group…

Doug Gowans

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