Thanks for choosing QNAP.
The WD20EARS/WD20EADS you used are not compatible with any RAID devices which caused this issue.
Please see the following solution.
1. See the following SOP to recover your NAS firmware.
2. Boot up the NAS with 1 signle drive and then backup all data out and then reinstall the NAS as RAID 5 with 3 fully compatible disks(http://www.qnap.com/en/?lang=en&sn=3877).
It appears my WD Greens (same as OneWhite), may be the root of the problem. Trouble is that according to the HDD compatibility list they are compatible, but there are potential problems so they're not recommended:
Note5 (WD Green & Seagate Green)
These hard disk drives have passed QNAP lab's initial verification of compatibility. However, because many users have reported unstable experience with these hard disk drives, we do not recommend using these had disk drives with QNAP products. WD10EADS-00P8B0 and WD15EADS-00P8B0 are not suggested because of slow performance and stability issues.
I'll update my drives at some point, but I had these two drives already so used them.
Anyway the upshot is that I simply rebooted the NAS. As I had to turn off the NAS anyway, as support had suggested, I thought I'd give a reboot a go first. When it came back up it stated that it was rebuilding the RAID 5 again. I logged off and disconnected anything that might be connected to it via the network (last time I left the admin interface open showing the progress), and let it do it's thing. This morning I have a GOOD RAID 5, great, but no data... in the shares.
I've found it in a folder called /share/MD0_DATA/. It's all there and I'm going to go start borrowing HDDs to take it all off before doing anything else.
But I was just wondering if that was needed or whether I could move the data from there to the shares and carry on all RAIDed up and ready to go?
Bit long I know sorry, but I like to try to get as much info as possible out there for better help!