This is based on what I've done so probably you can pickup some pointers.
My company is using a LS Pro Duo.
We had one of the drive failed.
The only way to know is that if the users cannot connect to the LS Pro Duo.
However, based on the user's problem description, the IP of the LS Pro Duo was valid.
So we access into the LS Pro Duo's IP address and it was able to accessed to the LS Pro Dup console's page.
On the header of the first page that we logged on, we are able to see that there is a RAID Error.
Then we clicked on Disk Management to see that Disk X was not ticked.
We advised one of the user to remove Disk X and replaced it with another model if similar size.
Once he've done that, we again access the console page of the LS Pro Duo, click on Disk X and then proceed to Restructure Disk Array.
After couple of hourse, we re-logged in to see that the error mesaage was no longer there and checking on Status, it was unning in RAID 1.
Here's my 2-cents.
tanjl