Installation guide

Introducing XenServer

attacks. Xen is fully open to scrutiny by the security community and its security is continuously tested. Xen

is also the foundation for a Multi-Level Secure System architecture being developed by Citrix, IBM and Intel.

Xen was originally developed by the Systems Research Group at the University of Cambridge Computer

Laboratory as part of the XenoServers project, funded by the Engineering and Physical Sciences Research

Council (EPSRC), the main funding agency in the United Kingdom for research in engineering and the

physical sciences as well as the managing agent on behalf of the other Research Councils for High Perfor-

mance Computing.

1.4.2. XenServer extends the power of Xen virtualization to server

clusters

XenServer allows IT administrators to flexibly assign up to 16 64-bit x86 servers into a single resource

pool of server resources. Multiple pools can be managed from a single XenCenter management console.

A resource pool is a tightly coupled collection of servers whose resources are virtualized to host a set of

Virtual Machines. Servers in a resource pool monitor the configuration state and availability of their peers.

XenServer management state is also replicated across all servers in a pool, with the benefit that failure of a

pool master can be quickly remedied, since any node in the cluster can replace the failed node. Using the

XenServer clustering architecture, the workload of a cluster can be protected from server failures, through

a unique combination of shared storage, Xen virtualization, and replicated state management between

servers in the cluster.

Virtual Machines assigned to a resource pool are automatically mapped onto the physical resources of the

pool, but IT administrators retain full control of resource assignment, and full visibility into each system and

each Virtual Machine, including the ability to manually place workload on specific servers, and drill down

into each server within the pool to get a precise view of each server's resources and the Virtual Machines it

hosts. At the simplest level, all the administrator needs to do is assign a Virtual Machine or a set of Virtual

Machines to a resource pool. XenServer manages the rest, including the assignment of physical resources

from servers in the pool to host the VMs, and ensuring that administrator policies for resilient restart of VMs

are implemented. XenServer ensures that the overall utilization of the resources of the servers in the pool

is maximized, to deliver lowest possible TCO.

Of course, if you want to assume full control, XenServer gives you the ability to manage each resource for

each VM, but most users will appreciate the simplicity of the "drag and drop" interface for VM provisioning

with guaranteed VM performance, automated VM storage and network management, and the use of policies

for automatic restart on failure of physical components of the cluster.

1.4.3. Powerful VM storage management and clustering

In most datacenters, storage is managed as a shared, separately administered resource independent of the

different server applications and OS types that make use of it. The rich set of choices for datacenter storage,

and the emergence in its own right of storage virtualization as a powerful technology that reduces TCO

for storage, leaves IT managers with a bewildering set of choices for storage and storage management.

XenServer aims to simplify the management of diverse storage technologies for virtualized infrastructure.

It does this by

• providing a simple plug-in interface for each of the different storage technologies used in the datacenter

today, extensible by storage vendors

• hiding the complexity of storage-related operations on each technology, for example snapshotting for VM

backup