I was looking at the Exchange 2010 Mailbox Server Role Requirements Calculator and it says: How many lagged database copy instances per database do you plan to deploy within a DAG? Lagged database copies are an optional feature that can provide protection against certain disaster scenarios (like logical corruption). Lagged database copies should not be considered an HA database copy as the replay will delay the availability of the database for use once activated. While technically there is no limit to how many lagged copies you can deploy within a DAG, the calculator limits you to a maximum of 2 copies. Anyone know why it sets the limit at two copies? I think I'd like to keep five. Is there any reason not to? Thanks.

Why do you think you need any lagged copies? :)

If the DB becomes corrupt, I'd like to be able to make a lagged copy the active DB. I am planning on weekly or bi-monthly backups too.

How many copies of each database do you have now? Personally, I would avoid using lagged copies. I agree with Tony: http://thoughtsofanidlemind.wordpress.com/2010/11/19/thoughts-on-lagged-database-copies/

As for why the calculator limits you to 2, it's probably a combination of 1) most people don't deploy more than that and 2) it would make the calculator too complicated (calculating the disk space required for all the databases and logs... you can do the math yourself) If you are already taking point-in-time VSS backups I don't see the point either, unless you feel your restore times are really slow (in which case, why bother taking those kinds of backups?) Lagged copies make sense if you have decided to go with "Exchange Native Protection" (marketing lingo for 'don't make any backups and rely on multiple database copies on multiple servers)' *and* if you still need to be able to roll back in time. Logical corruption that replicates across all live copies is very rare. Administrator error that replicates everywhere is sometimes more common :)

and its worth noting that Microsoft IT doesnt use them either.