Looks like my USB finally gave up. Just one day I couldn't access OMV. It stopped booting at "can't access tty; job control turned off". I thought it would be faster to install OMV 0.5 from scratch than figuring out the problem. It installed fine on an old 80 GB drive, and my LVM setup was still intact.
I see a clear improvement in memory and CPU usage, but I don't know if that's due to the new version of OMV or having the OS on a hard drive?
When I tried doing anything else with the USB drive afterwards it was bricked. Anyway, I thought it did a good job for 1.5 years RIP :cry: