I was getting this error ("Stderr: 'iscsiadm: No portal found.\n'"). It turned out that I had both tgt and iscsitarget installed, and both were trying to run a service on the same port. Cinder was setting up a tgt target, but iscsiadm was connecting to the iscsitarget service and not finding it.
The fix was:
apt-get purge iscsitarget
After that, I was able to attach a volume to a VM using Horizon.
I was getting this error ("Stderr: 'iscsiadm: No portal found.\n'"). It turned out that I had both tgt and iscsitarget installed, and both were trying to run a service on the same port. Cinder was setting up a tgt target, but iscsiadm was connecting to the iscsitarget service and not finding it.
The fix was:
apt-get purge iscsitarget
After that, I was able to attach a volume to a VM using Horizon.