To all who replied to my distress signal, The repair turned out to be pretty painless. In two ways:
First, getting quality advice from all of you sans the roasting I deserved ;), and Second, gdisk fixed the gpt header and partition table easily (details below). After that, I rebooted, zfs recognized the disk, and then it started a resilver automatically. It was done a few minutes later, and now everything’s back to normal. Gdisk noted that both the main gpt header and main partition table were damaged, but the backups were ok. I bypassed gdisk’s offer to use either the current gpt or to create a blank gpt, because I didn’t understand exactly what “current” or “blank” meant. Instead, I invoked the recovery & transformation menu with “r”. Then I used “b” to rebuild the damaged main gpt header with the good backup, followed by “c” to restore the partition table from the good backup. I then printed the partition table. It looked exactly like the partition tables on the other disks of the same make and model in the zfs pool (modulo what looked like a unique zfs partition name). That made me comfortable, so I wrote the changes to disk, rebooted, and found everything back to normal after the resilver. Appreciate all the help. Thanks! John
