Exchange replay lag time & Truncation lag time

To understand replay lag time & Truncation lag time, refere to the below articles:

 

Add a Mailbox Database Copy

http://technet.microsoft.com/en-us/library/dd298080(v=exchg.150).aspx

Managing Mailbox Database Copies 

http://technet.microsoft.com/en-us/library/dd335158(v=exchg.141).aspx

Configure Mailbox Database Copy Properties

http://technet.microsoft.com/en-us/library/dd351151(v=exchg.150).aspx