ReadyNAS RN4220 wont boot up after shutdown from WebUI

The 4220 has a single PCI-e slot, normally containing the 10GbE NIC.  It's an 8x form factor, if I recall correctly, but that doesn't mean it's 8x functionally.  To support the NIC, it likely is 8x, but I went with a 1x video card to be safe.

Actually, each volume will work by itself in a 6-bay NAS.  It'll complain about the missing volume, but you can recover the data.  Do you have an old log .zip file you saved?  It will contain the information you need on drive order.  Just be aware that in the logs, the drives are numbered 1-12 in some and 0-11 in others.  If you boot in read-only mode, it won't do any damage if you have to experiment.  Just be sure to mark the drives as you remove them so you don't get everything mixed up.

If you want to keep using two 6-bay ReadyNAS, you can simply DESTROY the missing volume on the one containing the original main volume.  The other will be trickier due to apps (if you have any) and user private shares, which will be missing.