S.M.A.R.T started reporting errors, and when I restarted guests they randomly didn't boot and so on. I couldn't copy the guests to a new disk, so I had do replace the disk and install new guests.
No extents. Just a single VMDK on a single disk, KISS on a home server/white box.
No, i don't have any backups of the home servers "vacation movies" disks. It's simply too expensive to backup 11TB on "private cash" basis.
I did count on loosing one disk or so, even though i replace the disks once every second year. But here it's obvously something very different that has happened.