RAEDYNas 104 inactive Volumes

Both data and data-0 contain your volume.   They are two sections of what should be your data volume, but the OS can't figure out how to put them together into one and can't call them both data.   Doing anything at all (including any more reboots) without knowing what you are doing may significantly reduce the likelihood of recovery.  StephenB​ has successfully guided many through your situation.  There is a possibility that a file or few is corrupted, but intact recovery of most is usually possible if you have patience and the volume is RAID5 (as yours is), not RAID0 or JBOD.  If you've been ignoring one drive failure (knowingly or because you don't "check in" with your NAS often enough and/or have email alerts set up), then that chance goes way down if it had a second drive failure.  The log will let you know your situation.

That recovery, however, may include the need to purchase rather expensive RAID recovery software and will most often require recovering the files to another device.  So, hopefully, that USB drive will hold it all.  It may also require that you have a Windows machine on which to run  it.