XenServer resource pool overview
A Citrix XenServer pool is a group of XenServer hosts and allows you to view multiple servers as a single resource, enabling flexible deployment of virtual machines based on the resource needs and business priorities.
A pool is comprised of multiple XenServer hosts bound together as a single managed entity. When combined with shared storage, virtual machines (VMs) can be started on any XenServer host in the pool that has sufficient available resources such as CPU or memory, and then dynamically moved between hosts while running, using the "XenMotion" feature with minimal downtime. If an individual XenServer host suffers a hardware failure, you can restart the failed VM(s) on another host in the same pool.
If the High Availability (HA) feature (only available to XenServer Advanced Edition or higher) is enabled, VMs are automatically moved to another host in the event of a host failure.