Where does it say that? Did you run a SMART test? If so did you run it on the spare or on the drives that are in your zpool? Are you sure it's not your spare which has the disk errors? Double, no triple check the gptid of the disk that is showing failures before removing that drive. Because you have Raid0, if you remove the wrong disk, your entire pool will be lost. Since your system is online now, I would first backup all the important stuff to another machine and then worry about replacing drives.
I've not run any tests as I'm concentrating on syncing my backups, but it tells me on the status 'bulb' thing.
