Mmm...the RPi is overloaded with rrdcached activity, which is part of the statistics collection. If you can get to it, I reckon turning off statistics collection might just relieve the cpu from 100% load. I've had several goes at my RPi1, and I am just figuring out the issues (mainly RPi can get overloaded very easily). After rebooting my RPi, it cannot even get itself attached back on the network!! So, I'll have to start over with another new OMV SD card (again). So maybe by tomorrow, I'll be another step closer to a slow, but working, OMV install.
Hope this hint helps.