I have my unraid on an UPS as well as my router (different UPS). Here's my delima/question, I'm in Houston and I'm going to be without power for an indeterminate amount of time. I didn't think ahead and get some media off of my server and on to my iPad before I lost power, so here's my question. Would it be safe to power up my unraid server (If I did the math right I should have about 20 minutes of sustainable power) and my router hook my laptop via ethernet and transfer media  then do a safe shutdown? 

It would be no different than running it on "live" electricity. With the exception* that it will obviously run out. 

 

* the longer the batteries sit uncharged, the higher percentage chance they will ultimately fail and need to be replaced.

I doubt you will have enough time to actually do anything meaningful. This is probably a tall order, and possibly out of the question given the local circumstances, but it would be much preferable to use a source of electricity with a more useful runtime. A large enough inverter for your car, or a small gas powered inverter generator are much better options if you can swing it.

 

Bringing up the server with all your dockers and stuff without an active WAN connection is going to delay startup by several minutes to begin with, then by the time you can get in and start transferring, it's going to be time to start shutdown so you don't run completely out of battery.

 

Now... IF you have a high tolerance for risk, and IF you have electrical skills, and IF your battery backup runs on a single 12V battery, and IF your particular UPS allows islanding (some won't start without 120V after they've been shut down) and IF you have fuel to spare in your car or a second car that is unneeded at the moment, then you could possibly rig up either a spare car battery or jumper cables from your vehicle and get significantly longer runtime.

 

(*disclaimer*)

I AM NOT RESPONSIBLE FOR YOU BLOWING UP YOUR HOUSE, CAR, OR COMPUTER EQUIPMENT IF YOU DECIDE TO ATTEMPT THIS.

Personally, looking at the news and the situation in Texas, I reckon lack of media to watch would be pretty low down on my list of priorities.  Hope all you Texans are OK over there!