In Exchange 2007 you may find yourself in a situation where you will need to manually resync an LCR or CCR backup database - either the backup database is corrupt, gone out of date or perhaps you have performed an offline defrag on your production database. To do this first suspend your copy by right clicking on the storage group and clicking Suspend Storage Group Copy. This only takes your backup copy of the database offline, users will be able to continue working however this process will create high disk activity and users may experience their outlook clients hanging so if possible do this out of hours.
The powershell command to perform the resync is:
Update-StorageGroupCopy "KBOMB Storage Group" -DeleteExistingFiles
IN A CCR CLUSTER ONLY RUN THIS COMMAND ON THE PASSIVE NODE!
However Microsoft have made a GUI to do this as well... you can simply right click on the same storage group and click Update Storage Group Copy. However make sure you tick the box "Delete target transaction logs".
An article I found by Raphael can be very handy when a CCR cluster is down and everyone is in panic mode!