SNMPv3 has been available in CA PM from the get-go. As in since it was initially released. There is no way to remove this functionality either (not that you would want to!).
The differences between PM and eHealth (if that is where you are coming from) are:
- Native support for SNMP v3
- No need for the SNMP Research SNMPv3 module to be installed
- Setup of SNMP is performed through profiles
With the use of SNMP profiles, there is a "separation" in configuration between devices and their SNMP association. As in you can have multiple SNMP profiles defined and a subset of these are used/associated with devices through their monitoring profiles. Therefore, if you are polling a device using SNMPv1/2c, you can re-associate the device with a new SNMPv3 profile and continue on polling. You will get the same information as you have polled before (unless you fat finger the SNMPv3 profile configuration).
Also, you can try to minimise the data outage during the swap but you can't guarantee that you drop perhaps one poll cycle of data to the device in question as the SNMP polling setup moves over (depending on how frequently you decide to poll the device in question).
There will be no loss of previously gathered performance data for the device (unless you deliberately go and delete the device and re-discover it, which is unnecessary!).
Ed