Measure database availability beyond 99.9%

Hi,
we are looking for a tool to measure and report the availability of our databases in the HA range, i.e. with high precision. At this time we are only interested in the database state, not whether the customers can work.
The database versions involved are 9.2 - 10.2, 11 coming next year. All editions: SE1, SE and EE.
So far, we have been using EM Grid Control, but beyond 99,9% this is not precise enough. Too many failures of the agent/the Grid Control system rather than the database and too much time between "database back up" and "agent notices that database is back up". A switch in the failsafe clusters takes less than a minute and should be reported to the second, 
if possible.
We can get startup time easily from a database trigger or the alertlog, but have not good way to measure shutdown time so far. Is there something good available (free would be nice) or do we have to build it ourselves? 


Thanks for your help.


Regards
Ingrid Voigt
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http://www.freelists.org/webpage/oracle-l

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