Failed over to a Aysnc Replica and now previous primary replica(Now Secondary) is in NOT SYNC state

Question

Hello All,
Here is my situation :
3 Nodes in an AG configuration, and its a multi-site cluster. Sync commit between 2 nodes in one DC and Async commit to a node in the DR DC. 
AG is failed over to the Async Replica which is the DR site and all the databases comes up fine and application also can connect using the listener.
When checked the state of secondary databases, its in NOT SYNC mode. Data is suspended automatically.  I can resume data movement to fix the problem, but was curious why this will be in NOT SYNC mode?
Thanks in advance.
Thank you,
Anup
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Answer 1

Hello Anup,
The reason this happens is because of the forced failover needed to be used when moving to an Async replica. It will cause all other replicas to become suspended due to the fact that it is never known if data loss will occur or not.
It might not make sense right now, but think about a situation where the databases are not synchronized and failover is forced (it has to work in all situations). There may be a good bit of data on the primary replica that has not yet made it (or partially)
to the async secondary. It wouldn't make sense to negotiate the primary back down (after all, it's the async one) and undo valid transactions. It also allows for a database snapshot or other method to be done on the old sync primary which could be used for
DR purposes to get those valid transactions and data out.
BOL Doc:
http://msdn.microsoft.com/en-us/library/hh213151.aspx#ForcedFailover
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