Extility is built using an inherently scalable architecture. The main components are: a user interface and control system, one or more XVP clusters, a storage subsystem made up of several redundant storage nodes, and a network subsystem.
Nodes and control system
The user interface and control system provides the portal for end-users and operations staff, implements the business processes and operates the link to the billing system. It consists of a redundant pair of XVP controllers which can control multiple clusters. Each cluster supports up to about 16,000 cores, but a lower limit per cluster may be desirable. An XVP cluster is made up of many XVP nodes, controlled by a redundant pair of XVP managers; these are combined with the XVP controller in single cluster configuration. Each XVP node is a high specification diskless multi-core machine running customer virtual machines. We recommend using nodes with at least 16 cores. Each node runs the Xen hypervisor (though the system is designed to support multiple hypervisor vendors), which securely partitions the node at a logical level into virtual machines: one host and multiple guests. The host operating system on each node is Linux, running our node control software. The guest virtual machines run the end-user operating systems, and are instantiated by the controller via the node control software.
Storage
The storage subsystem consists of one or more high availability storage clusters, such as Oracle 7400 series filers or 3Par F-Series or T-Series arrays. These provide iSCSI LUNs to the end-user operating systems, looking just like physical disks. However, the storage system allows for instant clone and restore, as well as thin-provisioning, giving huge savings on required storage in addition to maximizing reliability.
Network
The network subsystem configures the layer two switched architecture and external firewalls. It also provides IP address management, tracks bandwidth, and provides reporting and billing. A typical configuration consists of switched 802.1Q VLANs, trunked to the XVP nodes. Three physically separate networks (A, B, C) carry customer traffic (which itself may consist of multiple VLANs), storage traffic, and management. Each XVP node has six gigabit ethernet ports spread across three gigabit ethernet cards, with the networks split so that failure of any card still leaves a connection to each network. Only appropriate VLANs (public network plus the customer’s own private VLANs) are visible to guest virtual machines. Two top-of-rack switches per rack aggregate traffic on a 10 Gig-E capable network, to which the storage subsystem is directly attached.