Comment 4 for bug 797770

I've managed to reproduce it on current trunk. Affects only impl_carrot.

Easiest setup i found to do it:
1. Set --volume_driver=nova.volume.driver.FakeISCSIDriver and --rpc_backend=nova.rpc.impl_carrot
2. Create project "proj1" with admin "admin"
3. Run nova-api, nova-scheduler and nova-volume
4. Burn it with:
echo -n '{"volume": {"snapshot_id": null, "display_name": null, "display_description": null, "size": 1}}' > create-vol.json
ab -H "x-auth-project-id: proj1" -H "x-auth-token: admin:proj1" -p create-vol.json -T 'application/json' -c 10 -n 1000 -v 4 http://127.0.0.1:8774/v1.1/proj1/os-volumes

nova-scheduler fails with exactly the same error in no time. May be, we should remove carrot support once and forever?