Hi Castleknock,  I found this information in kb54528,not sure whether it helps :  When the Celerra with the primary Usermapper server is down, secondary Usermapper servers will use their cache to map existing users/groups. However, any requests to map new users/groups can only be handled by the primary Usermapper. If the primary is not available, new users/groups will not get mapped and will thus be unable to access CIFS shares. Existing users may experience some delay in response or intermittent timeouts if when have new users/groups try to access CIFS shares when primary Usermapper is inaccessible.  Thanks Jyothi
question.  If a secondary usermapper is split from its primary, is there a timeout value that the secondary purges its cached results from the primary or does this remain persistent ? The reason I am asking the question is people are doing DR testing and I want to understand any implications for the usermapper function when comms between the primary and secondary usermapper roles are cut. One I suspect will occur is if a person accesses data for the first time on secondary usermapper and it cannot communicate with primary is no SID/UID entry created ? 
usermapper cache timeout question