Thanks, for the info, I have been able to rebuild the drive, and everything looks good.
I still don't know why it happened in the first place, the Unraid server is a Dell PowerEdge R510 (with a SAS backplane), using a H200 HBA (in IT mode), and the server room was locked. I were copying the data on the network to the new drive, when it got the problem.
If anything happens again I will not restart the system without making a diagnostics zip file.
Thanks again.