Hi !
We have 2 clustered servers, each server holds the mailfile, private addressbook and journal of each BB user.
Last week one clusterserver was down. Everything worked but searching the addressbook from the handheld took up to 1 min till a result was displayed.
Is there any known cluster problem in case of of server is down ?

could you please write your Domino and BES version?
Usually the failover is working fine.

LD 6.5.4 and BES 4.1.3 .
Failover works, but search lookups in the addressbook take up to 1 min .

Do you have multiple address book setup in DA?

Good thing that the address lookup is not non-responsive but just a delay of 1 minute. If I were you I will only worry about it if the lookup returns nothing or timeout.

The cause may be due to the additional probe to the other active cluster member mail server that cause the additional delay; which in turn adds more load on the thread pools that serve the assigned mail servers.

Check to see if there are hung threads in the MAGT log file (keyword is "No Response"). I would suspect that there are some and they are with WaitCount of 1 and 2 but they eventually recovered.