I had a 4 disk raidz1 array of four identical drives, and one of them was having problems so I pulled it. I was able to resilver to learn more about the drive specs, so I ran some tool that was allegedly read-only. It was not read-only, and after running it, all of the partitions tables of all three disks that were still in the machine were missing. Scared the shit out of me. I got the bright idea to put the failling disk back in and dd the first few blocks of it onto each of the three that had their partition tables wiped, and OMG, it worked. I was able to resilver them, even with the failing disk limping along, and get back to 100% data integrity.