I am running a 2 server collective, the current data archive version is 3.4.390.16/18.
I am planning for the upgrade to 2016 R2.
The "PI Data Archive 2016 R2 Installation and Upgrade Guide" tells me to upgrade the secondary server(s) first.
My experience with collectives is limited and what I don't see is any reference to data loss or approximate duration of the upgrade if there is data loss.
With HA (collective) functional, is the upgrade possible without any data loss (PI to PI and OSI Monarch PI Archiver are the primary interfaces/sources of remote data)?