How can I clear the errors and announcements from all of my nodes?

You can issue the following to clear announcements:

snmpset -v2c -c"[snmp write password]" -m [MIB file location] [node IP address] castorClearAnnouncementsAction = 'y'

You can issue the following to clear errors:

snmpset -v2c -c"[snmp write password]" -m [MIB file location] [node IP address] castorClearErrorsAction = 'y'

You can easily extend this in a loop to clear the announcements and errors in a whole cluster.

The script snmp-castor-tool.sh in our Tech Support bundle https://support.cloud.caringo.com/tools/Tech-Support-Scripts-Bundle.pdf has the ability to do this easily with the -E and -A options.