Hi, I am having this problem, but the wiki page was removed.
Here is what happened:
1) a few disks are USB
2) accidently unpowered external USB hub while Unraid was running
3) Unraid got upset
4) repowered hub and rebooted
5) 2 disks are "Unmountable"
6) did xfs_repair on sdX1 for both drives, xfs_repair was successful
7) Unraid still says unmountable
8 ) reboot
9) Unraid still says unmountable
10) stop array, start array with those two disks as "none"
11) stop array, start array with the disks configured again
12) Finishes, Unraid still says unmountable, but changed from red X to blue square
13) Parity wants to restore, allow it.
14) Parity restore finishes, Unraid still says unmountable
Update: Apparently I was most of the way there. To finish:
15) xfs_repair the drives again after parity restore
16) reboot