Citrix XenServer 6.2 goes open source

Free at Last!

Licenses and Consequences

In the course of the 6.2 release, Citrix changed the licensing model from a per-server to a per-socket model that costs $US 500 per socket per year. The price is roughly equivalent to that of the previous Enterprise Edition but now includes Subscription Advantage and premier support. These were options that customers previously had to purchase separately. Alternatively, Citrix offers a perpetual license for US$  1,250, but customers do have to renew the contract for software maintenance every year.

If you previously had a server license, you can exchange this for a two-socket license. Whereas previous versions offered a different feature set depending on the license, the one version now available includes the full feature set.

Besides the benefit of being able to request support, the only feature that distinguishes the use of XenServer with or without a license is patch management with the XenCenter graphical client. If you have a license, you can automatically roll out hotfixes and security updates to a pool of hosts in the graphical interface.

Manual Update

If you are worried that an unlicensed XenServer installation will leave you standing out in the rain with regard to patches, you can stop worrying: You can still patch at the command line. This approach is not quite as elegant, but it still works and is fully documented by Citrix (see "Patching Without a GUI"). Note that mixed operations with licensed and unlicensed hosts in just one (resource) pool are not possible – the complete pool behaves as if it were unlicensed.

Patching Without a GUI

The Citrix XenServer command line is a powerful tool for administrators who are familiar with it. As an example, I'll look at the process for importing a hotfix based on Critical Hotfix XS62E002 [10]. After downloading the patch to a computer with XenCenter installed, you can install the patch at the xe command line.

The first step is to install the patch on the pool master. To discover whether a host occupies the pool master role, you can check the Pool master property in the host's General properties:

xe patch-upload -s <Poolmaster> -u root -pw <Password> file-name=<Basis_path>/XS62E002.xsupdate

The command returns a UUID that you need later on:

59128f15-92cd-4dd9-8fbe-a0115d1b07a2

Then, all the machines in the pool need the hotfix:

xe -s <Poolmaster> -u root -pw <Password>patch-pool-apply uuid=59128f15-92cd-4dd9-8fbe-a0115d1b07a2

You can now check the success of the action: The following command should display the hotfix as installed on all hosts (listed by UUID):

xe patch-list -s <Poolmaster> -u root -pw <Password> name-label=XS62E001

This critical update requires a restart of all machines because you have updated the Xen hypervisor and its associated tools. Thus, you need to migrate active virtual machines to other hosts before patching. If successful, you will see fully applied in the pool properties after XS62E001.

Technical Innovations

Along with the significant licensing changes, the new XenServer version also comes with a number of technical improvements, which are not particularly groundbreaking but are evidence of a continuous development of the product. For example, scalability has improved.

With appropriate hardware, up to 500 virtual machines running Windows, or 650 running Linux, is possible per host [11], making this enhancement a boost for desktop virtualization. The manufacturer also has extended the list of supported operating systems. Besides new versions of the major Linux distributions, Windows 8 and Server 2012 are now supported; this support was previously considered experimental.

The "Performance Monitoring Enhancements Pack for XenServer 6.1," which added RRD metrics to the legacy XenServer version and had to be installed manually, is now an integral part of the new version and offers much better insights into the I/O throughput. Figure 3 shows a brief overview of the selectable metrics for a hard disk. XenServer stores corresponding performance indicators for a year in an RRD database that discards the details over time. If you want to process the data with other tools, you need to convert using rrd2csv.

Figure 3: New monitoring metrics allow a more detailed review of the performance parameters of hosts and virtual machines.

The new XenServer also includes a number of smaller improvements, such as support for new types of CPU, a PowerShell SDK revised for robustness, and optimizations that prevent DOM 0 from being taken down by excessive logging. Citrix also now uses a more recent version of the Xen hypervisor (v4.1.5).

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