Having recently pondered this very same thing I ended up going to ISO route. It’s the least painful route to upgrade. Just make sure you save a copy of your config with the secret seed so you can upload it after the fresh install of Fangtooth.
Using the ISO installer, we don’t get an upgrade option?
This is something I need to try and deal with once our classes are finished for the summer, need to move everything to scale and a simple way would be best to reduce downtime. That said, I have had to use a fresh install and upload the config a few times, always seems more scary than it really is. Only hangups I’ve ever had was with the AD joined servers which needed me to re-enter the account details and reload the directory.
I think it is time to refresh my boot devices too. Need to figure out what to do with one server that still uses USB drives, may just need to consolidate the data to one of the other servers and be done.
Do what I did, get on Amazon and buy a 2 pack of small (128GB) name brand SSD drives. That’s your new boot mirror. Fresh install to one, tell it it’s brother is the mirror, never worry about boot drives again. SSD’s that size are incredibly affordable now, the fact that they’re selling them in 2 and 3 packs is funny.
Unfortunately, buying SSD by the pair and using them in a mirrored configuration means that they will both hit their write limit at about the same time, making them less useful as a mirror pair. I either use 2 different make / model SSD (with different lifetime limits) or make sure that one of the 2 same make / model has more activity on it so they do not fail at the same time.