Virtual-Server Face-Off

VMware GSX Server 3.1
Now in its third release, VMware GSX Server offers two licensing levels: one for systems with one or two CPUs, and the other for systems with up to 32 CPUs. Like its competitor, GSX Server doesn't provide SMP support for the guest OSs and lets you run a maximum of 64 VMs concurrently on one host, depending on the resources the VMs require. GSX Server supports up to 64GB of memory on PAE-enabled Windows systems, and each VM can address up to 3.6GB of memory.

When I wrote this review, GSX Server officially supported only 32-bit hosts. However, the product also provides "experimental support" for 64-bit hosts, which basically means that they work but aren't recommended for use in a production setting. I expect VMware to announce official support for 64-bit host OSs after Microsoft releases Windows 2003 for 64-bit Extended Systems later this year.

GSX Server has a decided advantage over Virtual Server in the area of supported host and guest OSs. In addition to supporting all Windows OSs, GSX Server supports a variety of Linux systems as hosts, as you can see in Table 1. The product's client OS support is equally extensive.

If you've used VM Workstation or an earlier version of GSX Server, you'll find managing GSX Server to be a breeze. Figure 2 shows the Virtual Machine Console. Although it provides decidedly less information than Virtual Server's Administration Website, it's easier to use and noticeably more responsive.

Setting up new VMs under GSX Server is decidedly easier than using Virtual Server's piecemeal VM creation process. GSX Server's New Virtual Machine Wizard provides an easy-to-use interface that steps you through VM, VHD, and network creation. You'll probably want to install VMware's VMTools on all your VMs. VMTools provides a higher-performance video driver and enables cutting and pasting text between the VMs and the host.

VMware gives you several options for remotely managing GSX Server. The Windows-based Virtual Machine Console can connect to networked GSX Server systems. A Web-based management interface enables basic VM management functions, such as displaying and controlling VMs. You can also use a set of scripting APIs for Perl and COM, called the vmPerl and vmCOM APIs, respectively.

GSX Server supports two basic types of virtual disks: raw and virtual. Raw disks directly access a local disk partition. Virtual disks appear to the GSX Server host OS as a file. That file, which has an extension of .vmdk, stores the VM's entire file system. You can dynamically expand virtual disk files, or you can preallocate files when you create them.

GSX Server's undo disks let you save or discard all the changes in a VM at the end of a session, and virtual disks have a snapshot feature that lets you capture the current state of the virtual disk. GSX Server also supports differencing, but the associated process is manual and isn't nearly as easy to use as Virtual Server's differencing disk capability.

You have a choice of three types of virtual networking for GSX Server VMs: host-only, Network Address Translation (NAT), and bridged. Host-only networking restricts you to internal VMs that have no outside connections. The NAT option lets VMs connect to the outside network using the host IP address. GSX Server provides its own built-in DHCP server for host-only and NAT configurations. Bridged networking lets VMs access the outside network. Alternatively, you can choose None to disable the network hardware.

GSX Server lets you set up Microsoft Cluster service using shared SCSI VHDs. You can also transfer to GSX Server any VMs that you've created with VMware Workstation. One key advantage GSX Server has over Virtual Server 2005 is full support for USB devices—I could freely transfer data between GSX Server VMs and USB flash drives.

Performance
To test performance, I used the Sandra benchmarking software's combined performance index tests running on a fresh installation of Windows 2003, Enterprise Edition. I tested a variety of system performance factors, including basic display performance, memory access speed, and file-access and networking performance.

For Virtual Server 2005, I performed all tests on the local server that was running Virtual Server, using the Virtual Machine Remote Control Client running in full-screen mode. I configured the VM to use 384MB of RAM and used a fixed SCSI VHD so the test wouldn't be affected by dynamic expansion. The VHD was also on a different disk spindle than the drive on which the host OS was installed. To determine whether the Virtual Machine Additions made a significant performance difference, I first ran a set of tests without the Virtual Machine Additions installed, then ran another set after installing them.

In all the performance tests, the VMs running under Virtual Server were slower than those running under GSX Server. The CPU arithmetic test (Figure 3) shows Virtual Server lagging behind GSX Server by about 20 percent. The multimedia test (Figure 4) showed similar results. The other tests were closer, but GSX Server held onto a 17.5 percent advantage in file system performance (Figure 5) and a 5 percent edge in network performance (Figure 6). The presence of the Virtual Machine Additions gave a bigger boost to Virtual Server's file and network access performance than it did to the product's arithmetic and multimedia performance.

I configured GSX Server's VM to use 384MB of RAM and a preallocated virtual SCSI hard disk that was located on a separate physical hard disk from the host system's OS. I ran two sets of tests: the first without VMTools and the second with VMTools. As Figures 3 through 6 show, VMs running under GSX Server provide notably better performance than those running under Virtual Server. Considering that GSX Server is in its third release and Virtual Server is in its first release, it wasn't surprising that GSX Server is faster.

A Clear Choice
Both products are of excellent quality, and neither gave me any significant problem. If you need to run Linux or other guest OSs in a production environment, VMware GSX Server is the clear choice. VMware officially supports most popular Linux distributions. You can find more information about or download a 30-day evaluation version of VMware GSX Server 3.1 at http://www.vmware.com/products/server/gsx_features.html.

For those who have a Microsoft-only environment, however, Virtual Server 2005 is the better value. Significantly less costly than GSX Server, Virtual Server offers all the same capabilities for Windows guest OSs, albeit slightly slower performance. For more information about Virtual Server 2005 or to download a 180-day evaluation version, go to http://www.microsoft.com/virtualserver.