Its a ZFS volume on a RAIDZ2 volume which is used as a device extent in iSCSI.
PS. Problem is actually related to istgt and the fact that you need to stop and start the service for any changes to targets/extents to take effect, in this case the problem was that I'd deleted the device extent / target association but not restarted the service, after this was done I was able to delete the ZFS volume.
I second that! Destroy volume does not destroy it at all. I was able to gain access to my data again after I even deleted the partitions in GParted. Note that I did not reformat them. Destroy volume should make the volumes unusable. Now I will use Gparted to reformat all my drives just to see if that works.
With 8.0.1-RC1 I rebooted the PC and was able to create another volume. With build 7539 it is all broken and no amount of rebooting will fix it. Maybe in a few days that will be fixed.
"Destroys the given pool, freeing up any devices for other use. This command tries to unmount any active datasets before destroying the pool."
So I don't see where it states it's not really destroyed but I do believe you. I have been confused once before about this evil play on words. I also thought that when the Devs wrote this that when they destroyed a volume that they wrote to the front and back of the drive in order to make it look like no data was present. I'm sure I'm confused there as well, it's late and I'm old and tired. Nope, not drunk but give me time.
But I would like an easy option to physically erase the data on the drives. I'm not looking for a DoD Declassification feature, if someone wants that they would likely have to use a specific version of the software approved for that use. Us home users don't really care that much, but if we did then we are probably up to no good.