Free high availability: Create a XenServer virtualization cluster

With the free Citrix XenServer virtualization platform, it's easy to create a highly available virtual server cluster; here's how

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Installation of XenCenter is very straightforward, following a wizard. Once this is done, launch XenCenter. From this point forward, 99 percent of your administration of XenServer will be handled from XenCenter. XenCenter allows you to create, delete, start, stop, and administer virtual machines.

Step 3: Add servers using XenCenter
To administer each of the XenServer servers through XenCenter, you can simply "add a server." There are multiple shortcuts to this function, but for the sake of simplicity, using the top toolbar, select Server -> Add.

You will be prompted for the server IP and user/password credentials. Unless you changed something from the directions above, the user name will be root and the password will be as set during installation.

You may be prompted to verify the SSL certificate. <Accept>

Step 4: Create a XenServer pool
A pool in XenCenter is a collection of servers that you can manage as a group. If your physical servers are all of the same type, creating this pool will simplify administration. If you are intending to use XenServer's high-availability functions, a pool is required. By creating a pool and storing all of your virtual machines on an external share, to the virtual machines are freed from ties to any specific physical host. In the event of a physical host failure, the VMs on that host can be restarted immediately on another host in the pool.

The process for creating a pool is as follows: From the toolbar, select Pool -> New. You will be prompted to provide a name for the pool and an optional description. On the next screen, you will be asked to select a "master" server. This master server should be one that you have already connected to as a single server. Below the master server selection, you can add other members to the pool by selecting the check box next to the list.

To support high availability, your pool will need an external storage repository. You can create a pool without external storage, but doing so would be useful only for administrative purposes. If your VM's storage is hosted on the physical machine, and the physical machine goes down, there is no easy way of recovering that VM. Setting up your external storage will likely be the trickiest part of the installation. We cannot offer any help here, as this will depend on what equipment you are using. XenServer supports NFS, iSCSI, HBA, StorageLink, and CIFS.

We used an iSCSI target that could be easily referenced by each of the nodes created earlier. One could argue that the external iSCSI drive could fail, and you still have a single point of failure. In our case, our external iSCSI target is a RAID-6 with two controllers, so multiple failures would have to occur to lose the flat files that constitute the VM's virtual hard disk.

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