How to avoid synchronizing deletions back to the server after fixed server failure

Okay first some background info.
My server is running on a RAID1 system (mirrored drives). My whole Nextcloud is running on the RAID. It seems that around a year ago one of the drives was disabled due to a mismatch in the event counter. Ever since the RAID seemed to be running in a degraded state. Unfortunately I missed that or else I would have done something about it.

A few days ago I had to restart my server. However the RAID came back with the previously disabled drive that contained data that was over a year old. (And the other drive was disabled.) After Nextcloud was up and running again my Desktop client immediately began to synchronize everything and deleted a lot of files. That’s when I noticed something was wrong.

I was able to reenable the correct drive with the newer data and synchronize the other drive. My server is fixed now and from the web interface I can tell that Nextcloud contains the newer files again.

So here’s why I came to seek help:
Currently I have stopped the synchronization on my desktop client. And I’m wondering

  • if the client would synchronize all the deletions back to the server?
  • how I could prevent that from happening if that’s a thing

Note that I already made a backup that I could use just in case. But I’d like to avoid having to copy huge amounts of data (again).

Also I know that Nextcloud 15 is quite old. I am going to perform an update as soon as this issue is fixed.

Just wanted to report back. I reactived synchronization and everything worked well. My Nextcloud client didn’t seem to remember that there were any deletions and downloaded all files.

Not sure though if that’s always the case.