Comment 2 for bug 1020326

Actually the snapshot_id field means that the volume is created from a snapshot..
As I see when executing 'lvdisplay' :

  LV Name /dev/n-volumes/volume-528b8d8d-8067-436b-8677-3892369dce83
  VG Name n-volumes
  LV UUID gltzr2-2bWw-4vnV-CS4h-OICa-dlab-naKik2
  LV Write Access read/write
  LV snapshot status source of
                         /dev/n-volumes/_snapshot-6863b9ff-3604-4966-83cf-c7fbf73ee056 [active]

There is a flag that the volume has an active snapshot. But it seems nova is using a higher-level driver - tgtadm to load volume data, and this flag is not available there.

Maybe it would be nice if the volume metadata is being updated with a flag when a snapshot is created/removed, and this flag to be passed...

One solution is to check first if there is a snapshot with volume_id == vol_id of the volume to be deleted, and to show warning/error message before the actual delete attempt.
Or just to catch the exception and show a hint what the reason could be ..