A client enquiry brought out some interesting discrepancies in the way in which the Universal Driver Heavy (UDH) communicates the fact that it has stopped. The client in question wanted to be able to monitor the UDH to create alerts when it flipped into journaling mode so that corrective action could be taken.

Initially they thought that it would be enough to check the registry key value "MirrorInBackup" but they quickly ascertained that whilst this could be relied upon to show whether the UDH had been put manually into journaling mode, the registry key was not updated when the UDH flipped into journaling mode because of some failure.

Revelation very kindly provided us with the workaround - which was to check for the existence of journal files - if they exist then we're journaling regardless of what the registry value may say! As there are a variety of journal files this isn't a completely straightforward task but the required logic can be represented as follows :-



So with this scenario we can establish whether it is journaling AND whether the secondary server is back on line and being replayed to. Both scenarios mean that journaling is taking place but only one is potentially an error condition.