VMware in the SCS Facilitized environment
VMware is a virtual machine software system that allows a host operating system to run one or more virtual guest operating systems. For example, a system that is running Windows XP can use VMware to run operating systems such as Linux or Windows 2000. VMware does not emulate a machine it merely provides a set of virtual resources to the guest operating systems.
In the SCS computing environment, VMware is primarily intended for users who have either Windows or Linux as their primary operating system, but also need a low-level set of functionality that can only be provided by the other operating system. For example, a user who is running Linux may have a continuing need for access to Microsoft Office or some other application that only runs under Windows. The set of users that VMware is primarily targeted towards are those users who currently have two separate desktop machines (one Linux and one Windows) and who use both daily (although one is used more often than the other).
Users who only have an occasional need for an alternative operating system are still better served by either a dual-boot machine, or by using another machine temporarily. Since VMware carries its own licensing fee (in addition to the normal license fees for the operating systems run under VMware), VMware should not be used where the alternative operating system is infrequently needed.
While the installation of VMware (following the instructions provided by the manufacturer) is straightforward, there are some notes and recommendations that should be followed when installing in the SCS environment.
Before installing VMware, make sure that you:
- Have root/administrator access on your machine.
- Have sufficient disk space to install VMware and any virtual machines that you might want to run (20MB for the VMware software itself, and typically at least 10GB for a virtual machine).
- Have run netregister for any virtual machine that you may want to place directly on the SCS network.
- Have obtained a valid VMware license key.
- Have sufficient memory installed to allow for operation of the guest operating system(s) and the host operating system. In general, you should allocate at least 128MB of memory to the guest OS, and 256MB is preferred for better guest OS performance. Since the guest OS takes its memory from the host system, you should have a minimum of 256MB of main memory to run VMware, and 512MB to 1GB of memory is preferred.
Installation disk type issues
VMware supports several different disk models for guest operating systems, including running the virtual machine in a separate partition from the host operating system, and creating virtual disks in the file system space of the host operating system.
In general, if you are installing a new guest operating system and you do not have an existing partition with the guest system already installed, we recommend that you create virtual disks in the file space of the host operating system. On Linux systems, these virtual disks would typically be created in the /usr0 partition.
If you already have a second operating system installed in a separate partition, you may use this partition instead of creating a new virtual disk drive.
During the process of creating the new guest virtual machine, you will be asked for the size of the virtual disk for the guest OS. You should specify the maximum size you will need for this operating system. SCS Facilities recommends a minimum of 10GB for Windows XP and Linux operating systems. If you have a large amount of space available for virtual disks, you should increase the size of the virtual disks.
Note that VMware allocates the virtual disks in approximately 2GB increments and that these virtual disks are not allocated at their full size; the virtual disks will expand as files are created in the virtual machine. Thus, it is possible to allocate more disk space to the virtual machine than is currently available in the host file system. This should be avoided if possible, since the guest OS may fail if it cannot allocate needed disk space.
Guest operating system network issues
VMware supports several different network models for the guest operating systems:
- Bridged networking, where the guest OS has an IP address on the network that the host OS is connected to.
- Network address translation (NAT), where the guest OS is allocated a non-routable address by the host OS and is not directly on the host network.
- Host-only networking, where the guest OS can only communicate with the host OS over a virtual network.
SCS Facilities recommends the bridged networking option, which treats the guest OS as a standard machine on the SCS network. This requires that you register the guest operating system on the network.
During the installation process, the installation program will ask if you want to automatically configure your host operating system to allow the guest to access the file systems on the host system. SCS Facilities recommends that you do not select this option since the VMware tools uses the Samba file system to allow access to the host operating system. Samba has several known security vulnerabilities, and may cause your host operating system to be hacked.
Other installation issues
If you are installing VMware on a Linux host operating system, there are two different installation packages available to you: RPM and TAR format. SCS Facilities recommends that you download and use the TAR format package, since the RPM package may conflict with facilities-installed packages.
Known limitations & problems
In general, the VMware software works well and provides full functionality to guest operating systems. It should be noted, however, that what VMware provides to the guest OS is a virtual machine that has virtual hardware. This hardware does not usually reflect the specific hardware that is installed in the host machine.
For example, the host machine may have a graphics card that provides very high resolution display modes. The guest machine, however, will only see a VMware SVGA II display type, which may not support the same display modes as the host graphics card.
Also, since the host hardware is being shared between one or more virtual machines as well as the host OS, there may be resource allocation problems at any time. For example, if the guest OS attempts to play a sound while the host OS is using the sound hardware, the guest will receive an error that the sound system is not available and will disconnect the sound hardware. The user may reconnect the disconnected hardware and the guest OS will start using it again.
Overall usability issues
In general, VMware provides guest operating system performance similar to the performance of the host operating system. Typically, users should expect there to be a 10 to 15 percent reduction in performance between a VMware operating system and one running natively on the hardware.