7 High Availability

7.1 High Availability (HA)

You can set up HA in Oracle VM to guarantee the availability of guests if the Virtual Machine Server they are running on fails or restarts. When a Virtual Machine Server is restarted or shut down, the guests running on it are either restarted on, or migrated to, another Virtual Machine Server.

You can manage HA with Oracle VM Manager. To implement HA, you must create a server pool (a cluster of Virtual Machine Servers) and have them managed by Oracle VM Manager. HA cannot be implemented with a stand-alone Oracle VM Server.

To use HA, you must first enable HA on the server pool, then on all guests, as shown in Figure 7-1, "Enabling HA". If you enable HA in the server pool and then for guests, when a Virtual Machine Server is shut down or fails, the guests are migrated or restarted on another available Virtual Machine Server. HA must be enabled for both the server pool and for guests. If HA is not enabled for both, HA is disabled.

If HA is enabled, when you restart, shut down, or delete the Virtual Machine Server in Oracle VM Manager, you are prompted to migrate the running guests to another available Virtual Machine Server. If you do not migrate the running guests, Oracle VM Agent attempts to find an available Virtual Machine Server on which to restart the guests. The Virtual Machine Server is selected using the Preferred Server setting for the server pool when you create a guest in Oracle VM Manager:

• Auto selects an available Virtual Machine Server.

• Manual selects an available preferred Virtual Machine Server.

If you do not select a preferred Oracle VM Server when creating a guest in Oracle VM Manager, Auto is set as the default.

If there is no preferred Virtual Machine Server or Virtual Machine Server available, the guests shut down (Power Off) and are restarted when a Virtual Machine Server becomes available.

If the Server Pool Master fails, another Oracle VM Server is selected from the server pool to act as the Server Pool Master. The Oracle VM Server chosen to take over the Server Pool Master role is the first Oracle VM Server available to take the lock. To use the Server Pool Master fail over feature, you should make sure the Oracle VM Agent password is identical on all Oracle VM Servers in the server pool.

You can also dynamically change the Oracle VM Server which acts as the Server Pool Master without causing any outages.

If the Server Pool Master also performs the Utility Server role, and it fails, the Utility Server role is not moved to another Oracle VM Server. If you want fail over for the Utility Server role, make sure you set up more than one Utility Server in the server pool.

The possible HA scenarios are:

• If you shut down or restart a Virtual Machine Server in Oracle VM Manager, you are prompted which guests to migrate to another available Virtual Machine Server. Any guests which are not migrated, are restarted on an available Virtual Machine Server.

• If you shut down or restart a Virtual Machine Server at the Oracle VM Server command-line, Oracle VM Agent restarts the guests on an available Virtual Machine Server.

• If a Virtual Machine Server fails, all running guests are restarted automatically on another available Virtual Machine Server.

• If a Virtual Machine Server fails and no other Virtual Machine Servers are available, all running guests are restarted when a Virtual Machine Server becomes available.

Figure 7-2, "HA in effect for a Virtual Machine Server failure" shows a Virtual Machine Server failing and the guests restarting on other Virtual Machine Servers in the server pool.

Figure 7-3, "HA in effect for a Virtual Machine Server restart or shut down" shows a Virtual Machine Server restarting or shutting down and the guests migrating to other Virtual Machine Servers in the server pool.

To enable HA, you must first make sure all Virtual Machine Servers in the server pool:

• Use the same storage repository. This means all Oracle VM Servers in the server pool must have the same storage view. If the shared storage is OCFS2-based, the OCFS2 device /dev/sdd1 must be visible on all Virtual Machine Servers. If the shared storage is NFS-based, then all Virtual Machine Servers in the server pool must have client access to the same shared NFS source.

• Are in the same cluster.

• Are Oracle VM Server Release 2.1.2 or above.

• Have the cluster root configured from the Server Pool Master. The cluster root is specially designated shared storage used for heartbeating in the server pool (cluster). For example, the cluster root might be example.com:/OVS for an NFS cluster, or /dev/sdd6 for an OCFS2 cluster. The heartbeat file would then be located at example.com:/OVS/.server_pool_hb for an NFS cluster. There is no heartbeat file for an OCFS2 cluster as one is in-built in the file system.

• Have the cluster root mounted at /var/ovs/mount/root_sr_uuid and linked to the /OVS directory. All other storage may be mounted at /var/ovs/mount/other_sr_uuid.

  If you have created multiple storage repositories and set the cluster root from the Server Pool Master (see Section 9.2.5, "Setting the Cluster Root"), when you create a server pool from Oracle VM Manager, the cluster root storage repository is automatically mounted to /var/ovs/mount/root_sr_uuid and linked to the /OVS directory. Non-cluster root storage repositories are mounted to the /var/ovs/mount/other_non_cluster_root_uuid/ directory. All storage repositories are automatically propagated and mounted to other nodes in the server pool (cluster).

• Have a shared cluster root and link to the /OVS directory (not local), using clustered OCFS2 on SAN, or ISCSI storage, or NFS on NAS. If the default local storage is a local OCFS2 partition, it cannot be HA-enabled.

The following sections describe how to perform the configuration required to enable HA.

7.2 Creating Shared Storage

If you want to enable HA, you must create external storage to be used as shared storage for the server pool, then create a storage repository. See Section 8.1, "Preparing External Storage" and Section 8.2, "Preparing a Storage Repository" for information on creating the shared storage and storage repository.

7.3 Enabling HA

After you have created the storage repository, you must enable HA in the server pool and on guests. To enable HA:

1. Log in to Oracle VM Manager and enable HA in the server pool.

   If the server pool already exists, enable HA on the server pool. If the server pool does not exist, create the server pool and enable HA when you create it. See the Oracle VM Manager User's Guide for information on setting up HA using Oracle VM Manager.

   The server pool set up is verified and any errors are displayed in Oracle VM Manager. If there are no errors, the Oracle VM Agent on the Server Pool Master automatically mounts the storage repository set as the cluster root, and any other storage repositories, on each Oracle VM Server in the server pool (the cluster). When an Oracle VM Agent is started in the server pool, this propagation is repeated for that Oracle VM Server.

   The shared storage and cluster is configured, and the server pool is HA enabled.

2. When creating guests (virtual machines) in Oracle VM Manager, enable HA.

HA is enabled on the server pool and guests.