Ok, I too am having this problem (Datavolume doesn’t exist), but I am not set up in RAID5. I made the mistake of going with stripped (RAID0) under the impression that only a proper hard-disk failure could bring the system down 
I almost went with RAID 5, but it seems as though people haven’t faired much better with that, but i digress.
I am using a 2TB (4x500gb) WD Sharespace, and there appears to have been a minor hicup on drive 3. At first I could still see the Files, however after a restart I am now getting the “datavolume doesn’t exist” message. All drives appear to be ‘good’ but ‘unassigned’ under disk manager in the WD gui. I’ve enabled SSH, downloaded putty, and managed to log in as “root” with the default password “welc0me”. I’m not familiar with linux commands, and am only slightly tech savy. I’ve managed to run the “df” and “mdadm --detail /dev/md[0123]” commands, but as I am not using RAID5 (as others) I’m not sure where to go from there to, do anything at all to, access the files.
md2 and md3 do not appear active on my NAS, but i’m not sure if that’s because they’re corrupt, or because of the way RAID0 works… I was hoping some of you lovely folks who are more familiar with these commands could help point me in the right direction… it seems a rather steap learning curve for someone who cringes at the very sight of a command line interface 
Any help would be greatly appreciated 
-Brian
