If by any chance you are setting up a Xsan and are getting these errors:
"Error while writing settings (Duplicate registration)"
Then this apparently has nothing to do with the serial number.
It could be correct. But the problem is that Xsan has a database in which it stores the associations from hostnames an serial numbers. And this database can somehow seem to get mixed up if you install the same Xsan several times...
The thing to do is then to get rid of the database by entering the command:
on Metadata controllers as well as on all the clients.
Then reboot all of them and start anew.
This is how I got it working again.
The hint I followed was found here: