Parallels' Line
As of this writing, Parallels Server is the only game in town with production support for hosting Mac OS X 10.5 Server guests. However, VMware's Fusion, Sun's xVM, and other major market forces are pushing Parallels to stay on top of its game.

As an aside, we like Parallels Desktop 4.0 for Mac. The latest revision resolves a number of usability and performance issues. Unfortunately, the current version of Parallels Server, 3.0, shares a version number with the last generation of Desktop.

Parallels Server brings a world of flexibility to Apple's Xserve line. Mac developers and production shops are already utilizing Parallels for test and sandbox environments; the novelty of virtualizing OS X builds seems to supersede the limited feature set compared with other hypervisor platforms.

Mac-only IT shops will probably be pleased that the product allows them to consolidate multiple out-of-support Wintel and Mac G4/G5 servers onto one or two new Xserves.

Rolling Review

SERVER VIRTUALIZATION MANAGEMENT

Business value
We're testing virtualization management platforms to see if they lower hardware costs and save time and headaches for IT departments.

Reviewed so far
• Citrix Systems XenServer
Solid performance, many features, and now free. However, it lacks VMware's base of third-party support.

• Microsoft Hyper-V
Free, easy segue to basic virtualization for Microsoft shows. Features cost extra.

• Parallels Server for Mac
Currently the only game in town for Mac server virtualization, but its features are limited.

• Virtual Iron Extended Enterprise Edition
An easy-to-administer product at a very aggressive price.

Still to come
VMware ESX

More about this rolling review >>

Parallels performed well on Apple's top-of-the-line eight-core Harpertown Xserve with 32 GB of RAM, three 15,000-rpm SAS drives and a Fibre Channel connection to a legacy Apple Xserve RAID setup with 4 TB of usable storage. In addition, we tested an older dual-core, 8-GB Xserve. Intel VT-x is required; older 64-bit PowerPC Xserves can't run Parallels.

Parallels was a gracious host for Windows 2003 and 2008, Debian, and OS X Server guests with no issues. Guest performance was more than adequate on the Harpertown box, while our older Xserve faced resource constraints when asked to run three Windows 2003 instances. Apple doesn't provide iSCSI support in OS X, but a number of hardware and software vendors offer third-party products.

The strangest issue we encountered involved USB support for a Windows 2003 guest--a low-use server ripe for virtualization (in this case, a building management system) that required an old-school USB dongle to function. Parallels Server does not offer USB support or robust virtual LAN mapping for guests VMs.

Multiple virtual Parallels Servers can be managed from the Parallels Management Console. Like other VM management GUIs, hosts and guests can be paused, suspended, stopped, and reconfigured. Individual VMs can be accessed via detachable consoles. A stopped VM can be cloned.

However, there's no snapshot functionality, and performance prioritization is limited to optimization for either host or VM; there's no weighting between guests. There's also no live migration capability: VMs must be shut down and manually moved to a new host.

Parallels Transporter, the bundled physical-to-virtual conversion tool, performed with no issues in our tests.

Parallels charges just under $1,250 per host server regardless of configuration. This price is ideally suited for maximizing an eight-way Xeon Xserve, although it's not necessarily cost-effective for squeezing extra oomph out of a 2006 dual-core Xserve.

Joe Hernick is an industry analyst and former Fortune 100 IT executive.