Hosts and resource pools 编辑

This section describes how resource pools can be created through a series of examples using the xe command line interface (CLI). A simple NFS-based shared storage configuration is presented and several simple VM management examples are discussed. It also contains procedures for dealing with physical node failures.

Citrix Hypervisor servers and resource pools overview

A resource pool comprises multiple Citrix Hypervisor server installations, bound together to a single managed entity which can host Virtual Machines. If combined with shared storage, a resource pool enables VMs to be started on any Citrix Hypervisor server which has sufficient memory. The VMs can then be dynamically moved among Citrix Hypervisor servers while running with a minimal downtime (live migration). If an individual Citrix Hypervisor server suffers a hardware failure, the administrator can restart failed VMs on another Citrix Hypervisor server in the same resource pool. When high availability is enabled on the resource pool, VMs automatically move to another host when their host fails. Up to 64 hosts are supported per resource pool, although this restriction is not enforced.

A pool always has at least one physical node, known as the pool coordinator (formerly pool master). Only the pool coordinator exposes an administration interface (used by Citrix Hypervisor Center and the Citrix Hypervisor Command Line Interface, known as the xe CLI). The pool coordinator forwards commands to individual members as necessary.

Note:

When the pool coordinator fails, pool coordinator re-election takes place only if high availability is enabled.

Requirements for creating resource pools

A resource pool is a homogeneous (or heterogeneous with restrictions) aggregate of one or more Citrix Hypervisor servers, up to a maximum of 64. The definition of homogeneous is:

• CPUs on the server joining the pool are the same (in terms of the vendor, model, and features) as the CPUs on servers already in the pool.

• The server joining the pool is running the same version of Citrix Hypervisor software, at the same patch level, as the servers already in the pool.

The software enforces extra constraints when joining a server to a pool. In particular, Citrix Hypervisor checks that the following conditions are true for the server joining the pool:

• The server is not a member of an existing resource pool.

• The server has no shared storage configured.

• The server is not hosting any running or suspended VMs.

• No active operations are in progress on the VMs on the server, such as a VM shutting down.

• The clock on the server is synchronized to the same time as the pool coordinator (for example, by using NTP).

• The management interface of the server is not bonded. You can configure the management interface when the server successfully joins the pool.

• The management IP address is static, either configured on the server itself or by using an appropriate configuration on your DHCP server.

Citrix Hypervisor servers in resource pools can contain different numbers of physical network interfaces and have local storage repositories of varying size. In practice, it is often difficult to obtain multiple servers with the exact same CPUs, and so minor variations are permitted. If it is acceptable to have hosts with varying CPUs as part of the same pool, you can force the pool-joining operation by passing the --force parameter.

All hosts in the pool must be in the same site and connected by a low latency network.

Note:

Servers providing shared NFS or iSCSI storage for the pool must have a static IP address.

A pool must contain shared storage repositories to select on which Citrix Hypervisor server to run a VM and to move a VM between Citrix Hypervisor servers dynamically. If possible create a pool after shared storage is available. We recommend that you move existing VMs with disks located in local storage to shared storage after adding shared storage. You can use the xe vm-copy command or use Citrix Hypervisor Center to move VMs.

Create a resource pool

Resource pools can be created using Citrix Hypervisor Center or the CLI. When a new host joins a resource pool, the joining host synchronizes its local database with the pool-wide one, and inherits some settings from the pool:

• VM, local, and remote storage configuration is added to the pool-wide database. This configuration is applied to the joining host in the pool unless you explicitly make the resources shared after the host joins the pool.

• The joining host inherits existing shared storage repositories in the pool. Appropriate PBD records are created so that the new host can access existing shared storage automatically.

• Networking information is partially inherited to the joining host: the structural details of NICs, VLANs, and bonded interfaces are all inherited, but policy information is not. This policy information, which must be reconfigured, includes:

  • The IP addresses of the management NICs, which are preserved from the original configuration.

  • The location of the management interface, which remains the same as the original configuration. For example, if the other pool hosts have management interfaces on a bonded interface, the joining host must be migrated to the bond after joining.

  • Dedicated storage NICs, which must be reassigned to the joining host from Citrix Hypervisor Center or the CLI, and the PBDs replugged to route the traffic accordingly. This is because IP addresses are not assigned as part of the pool join operation, and the storage NIC works only when this is correctly configured. For more information on how to dedicate a storage NIC from the CLI, see Manage networking.

Note:

You can only join a new host to a resource pool when the host’s management interface is on the same tagged VLAN as that of the resource pool.

To join Citrix Hypervisor servers host1 and host2 into a resource pool by using the CLI

1. Open a console on Citrix Hypervisor server host2.

2. Command Citrix Hypervisor server host2 to join the pool on Citrix Hypervisor server host1 by issuing the command:

   xe pool-join master-address=host1 master-username=administrators_username master-password=password
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