Its apart of a Watercooling setup

If both servers are running TrueNAS (scale or core) the best way to backup a TrueNAS system to another is by using zfs replication.

https://www.truenas.com/docs/solutions/optimizations/disasterrecovery/

Video to get you started. https://www.youtube.com/watch?v=9gKZOAL7yeE

You could also do the following.

1. Setup site2site VPN connection of your choosing. IPSEC maybe.

2. Temporally do the setup of the secondary TrueNAS at Site 1, unless you are sure your Site 2 is good.

3. Configure the second TrueNAS to Pull data from the primary unit. FYI, pull configuration uses it’s own login credentials is a higher level of security.

4. Migrate the second TrueNas unit to the site 2. This way you aren’t diagnosing both the Pull config and VPN settings at the same time.

This would be perfect if I could fit 24th NVMe devices in this, but not looking to pay more then ~300-350 CAD in a device with no hdd/ssd

Is Nessus free for personal use?

I have been doing the same, buying the batteries off brand individually is a lot cheaper then OEM labeled/packaged.

Though what are your thought’s on a UPS lifespan not taking in to account the batteries themselves?

I myself have three APC BR1500MS2