Icehouse, the 9th release of OpenStack, is out! Thanks to the 1200+ contributors. OpenStack Icehouse
On a beefy machine (24 cores, 96 GB RAM, SSD), booting a single instance (from "nova boot"" to ACTIVE) takes seconds. However, when you try booting 20 instances in parallel, the last instance might not be ACTIVE for minutes! While you're waiting, you notice that the host's CPUs and disk are mostly idle and there's plenty of free RAM. While your instances are BUILDING, you wonder what's going on -- why's this taking so long?