Sometimes you have to do maintenance on the server and the time to reboot is part of it.
If you are turning off OMV to save on electricity maybe try setting up wake on LAN, it is my understanding then most systems will use less than 10 watts while waiting on WOL. And having a UPS can help with those random momentary power outages.
You may want to look into using PlexMediaServer which also does DLNA, though it takes a long time to initially create it's database, it seems to retain it between boots.
Hope you provided an alternative for your wife's pictures. Otherwise the OMV box may find it's way to the front yard!
Take Care and Good Luck!