Clustered pools 编辑

Clustering provides extra features that are required for resource pools that use GFS2 SRs. For more information about GFS2, see Configure storage.

A cluster is a pool of Citrix Hypervisor hosts that are more closely connected and coordinated than hosts in non-clustered pools. The hosts in the cluster maintain constant communication with each other on a selected network. All hosts in the cluster are aware of the state of every host in the cluster. This host coordination enables the cluster to control access to the contents of the GFS2 SR.

Quorum

Each host in a cluster must always be in communication with at least half of hosts in the cluster (including itself). This state is known as a host having quorum.

The quorum value for an odd-numbered pool is half of one plus the total number of hosts in the cluster: (n+1)/2. The quorum value for an even-numbered pool is half the total number of hosts in the cluster: n/2.

For an even-numbered pool, it is possible for the running cluster to split exactly in half. The running cluster decides which half of the cluster self-fences and which half of the cluster has quorum. When an even-numbered clustered pool powers up from a cold start, (n/2)+1 hosts must be available before the hosts have quorum. After the hosts have quorum, the cluster becomes active.

If a host does not have quorum, that host self-fences.

Where possible it is recommended to use an odd number of hosts in a clustered pool as this ensures that hosts are always able to determine if they have a quorate set.

Self-fencing

If a host detects that it does not have quorum, it self-fences within a few seconds. When a host self-fences, it restarts immediately. All VMs running on the host are immediately stopped because the host does a hard shutdown. In a clustered pool that uses high availability, Citrix Hypervisor restarts the VMs according to their restart configuration on other pool members. The host that self-fenced restarts and attempts to rejoin the cluster.

If the number of live hosts in the cluster becomes less than the quorum value, all the remaining hosts lose quorum.

In an ideal scenario, your clustered pool always has more live hosts than are required for quorum and Citrix Hypervisor never fences. To make this scenario more likely, consider the following recommendations when setting up your clustered pool:

• Ensure that you have good hardware redundancy.

• Use a dedicated bonded network for the cluster network. Ensure that the bonded NICs are on the same L2 segment. For more information, see Networking.

• Configure storage multipathing between the pool and the GFS2 SR. For more information, see Storage multipathing.

• Configure high availability on the clustered pool. In clustered pools, the heartbeat SR must be a GFS2 SR. For more information, see High availability.

Create a clustered pool

Before you begin, ensure the following prerequisites are met:

• All Citrix Hypervisor servers in the clustered pool must have at least 2 GiB of control domain memory.

• All hosts in the cluster must use static IP addresses for the cluster network.

• We recommend that you use clustering only in pools containing at least three hosts, as pools of two hosts are sensitive to self-fencing the entire pool.

• If you have a firewall between the hosts in your pool, ensure that hosts can communicate on the cluster network using the following ports:
  • TCP: 8892, 21064
  • UDP: 5404, 5405

  For more information, see Communication ports used by Citrix technologies.

• If you are clustering an existing pool, ensure that high availability is disabled. You can enable high availability again after clustering is enabled.

If you prefer, you can set up clustering on your pool by using Citrix Hypervisor Center. For more information, see the Citrix Hypervisor Center product documentation.

To use the xe CLI to create a clustered pool:

1. Create a bonded network to use as the clustering network. On the Citrix Hypervisor server that you want to be the pool master, complete the following steps:

   1. Open a console on the Citrix Hypervisor server.

   2. Name your resource pool by using the following command:

      xe pool-param-set name-label="New Pool" uuid=<pool_uuid>