Upgrade from 2.0 to 3.0 failed

Yeah, I'm thinking do a fresh install over this holidays.
My Plex, Emby, and Nextcloud folder reside on my RAID, that should be fine, right?
What o you use to backup the plugins settings?

I was debating whether or not to perform an upgrade on my NAS to 3. I've had a VM that I've been using to test things out with (like setting up Docker, etc) and a few other things. Decided to bring the VM up to what I have similar to the NAS (plugins etc) then take a snapshot and perform the upgrade. Sadly it failed. The two times I ran it, it failed in different spots. Gives quite a few errors regarding mdadm and no arrays, which isn't a surprise as I don't have a raid configured in my VM. ran a few of the apt-get commands (upgrade etc) then another image popped up saying to perform an omv-init or something like that. I did, it gave the same mdadm errors. I rebooted and it failed to boot, sitting at a grub recovery.

I'd like to avoid a clean install but I think I'd rather do a clean install over quite possibly losing data.

On my NAS, the system disk isn't raided at all, but I do have about 7 disks set up in a single RAID 6 with the raid split up using LVM and everything is ext4. The RAID was configured within OMV and not the raid controller on the motherboard. I'm just worried it's going to be a real pain to get back to where I am now with all the plugins I'm using plus the raid config etc, file shares, etc.

Well, I give up with testing the upgrade. It "succeeded" once out of over 20+ attempts in my VM with numerous different additions/removals of plugins including all plugins removed. The one time it did succeed, Grub was still screwed up which is a relatively easy fix (took a bit of searching but finally figured it out). If I have this many problems with what is pretty close to a clean install, I'd hate to know what would happen with my NAS that's been running for over a year now.

I'm now going to focus my efforts on making a "clean install" as quick and painless as possible

i thought it is´nt possible to upgrade .... because of new systemd - method in Debian 8 ?????

I did a fresh installation, and it running wells.
I figured it may be a headache to troubleshoot issues for upgrades.
So far, I'm happy with OMV3.