ReadyNAS NV+ v2 crashed?

Hi! I own a ReadyNAS NV+ v2 containing 4x3TB hard drives in FlexRAID. A couple of days ago, I noticed that reading and writing was slow, so I rebooted the NAS. When it was back online, I could no longer access my files, and in the ReadyNAS panel the Volumes tab in System > Overview is empty (the disks were all green though). So I selected "Perform volume scan on next boot" and rebooted. This time it got stuck at 69% in the file system check on boot. I figured one of the disks might be broken, so I tried removing one at a time and booting. Removing Disk 1 got the NAS to boot again, however Volumes is still empty and my files are not accessible.

Checking the logs, I see lots of warnings lately about increasing ATA errors and uncorrectable errors in Disk 2. I also have a "Disk failure detected" warning in Sep 25, however I don't see which disk it refers to. My theory is that if one of the other disks failed in September, and another one just recently, this is why my volume is inaccessible. Could this be the case? Is there any hope of restoring the data? Is there any chance I could rebuild the volume if I purchase and install a fresh disk in the NAS? I know that I should have checked the health of my NAS more frequently, I guess I was naive to think it would notify me of any problems..

Anyway, since I've lost about 9TB of data I would really like to know if there is something I can do to recover it. Thanks!

(I can upload the logs if it helps, just let me know which one)