Error condition:
ExchangeGRE console returns error:
System.Management.Automation.RemoteException: Database 'DBNAME' is offline.
+ CategoryInfo: ResourceUnavailable: (0:Int32) [Restore-Mailbox], RecipientTaskException
+ FullyQualifiedErrorId: C023C151,Microsoft.Exchange.Management.RecipientTasks.RestoreMailbox
Cause:
Database ran out of diskspace and was dismounted.
During search process in recovery there is a temporary mailbox created in production database and items are recovered to it using restore-mailbox cmdlet. Depending on mailbox search options specified it can potentially move the entire content of a mailbox from recovery database to this temporary mailbox, and this could take up to two time of a source mailbox size storage space. So if it was 10GB at backup time, in worst case scenario of broad search criteria and .edb file with no whitespace the process would need 10 GB for transaction logs and 10 GB for .edb growth.