mongoDB replica set with PSS 4.4.1 to 4.4.26 upgrade

I have a upgraded a secondary in our replica set. Then the secondary node is waiting startup2 mode. I know this normal according to below documantation.

But i wanted to ask two question.
Our database size is almost 3.5TB and one of our secondary node deployed another location and bandwith is not enough for the 3.5TB initial sync.

So, is the secondary fetching all data from primary? (i mean initial sync) or checking/fixing data?
I thought, it will fix old version data to new version data in database. Because our data folder in my secondary node still 3.5TB. This is not like initial sync.

if initial sync mandatory, is it possible to work different minor version of mongo in the same replicaset. Because i started upgrade process in my secondary server. If initial sync is not mandatory, i will upgrade all replica set member.


depends on the configured sync source. You can check the official doc for when initial sync is needed.

i suppose initial sync is not dependent on mongodb version (if the version diff is not too big). a big version bump may have compability issues on replication logic. Better to follow upgrade guide (if any)

It is a bit confusing about the timeline:

  • How far are your PSS servers apart? were they setup together in the same room/building?
  • When did you move that “secondary”? Or was it already setup on far-site?
  • Before or after started the upgrade?

3.5GB data may take to test over 10 hours on an HDD. So be patient when the servers deal with the data. (I am not sure if it needs be tested, though). The logs should be telling what process is running.