I've now seen two sata controller failures thanks to zfs. One on my own machine amd one on my parents. Both presented as if a drive failed but it was actually the port on the controller that failed. It'd start up fine but randomly reads (and probably writes) would just be corrupted and the disk would eventually stop talking. Changing disks wouldn't fix it, which is how I kmew it was the controller but replacing the controller made everything happy. It the resilvered with no issues.