Delaying munin notifications
Solution 1:
I don't really use Munin but as I see an unknown_limit
setting can be set for items/plugins which defines how many consecutive unsuccessful readings should occur before setting a value to "unknown".
Based on the Munin::LimitsOld module it defaults to 3, I think you should try to set or increase this number.
I have checked this on Munin 1.4.5.
Solution 2:
I achieve this by having munin notify, not directly to end-users, but into NAGIOS via NSCA, and having NAGIOS handle the notifications. This means I can use NAGIOS' (much more sophisticated) controls on notification delay, frequency, escalations and so on. Yes, NAGIOS is quite heavyweight just to be a notification engine, but you can then use it for qualititive (rather than quantitative) monitoring as well.