The Agent Health check feature in iMonitor shows a Warning icon in the Results column when run on a single server tree because of the Perishable Data status. This does not mean that the tree is not healthy or that the Agent Health check is not working as designed. Perishable Data indicates the amount of data that has not yet been synchronized to at least one replica. A single server tree, by its nature, means that the data is always at risk for catastrophic failure because there is no other place that the data is replicated. If you lose the hard disk, you lose the data.
If you don't want to view health check warnings about Perishable Data or Readable Replica Counts on your single server tree, you can turn off these health checks by editing the ndsimonhealth.ini file to change the following entries:
ring_readable-Min_Marginal: 1 or ring_readable-active: OFF
This turns off the warnings for Readable Replica Count and Perishable Data.