In the most common configurations, GSX Server creates virtual hard disks, which are made up of files that are typically stored on your host computer's hard disk. In some circumstances, you may need to give your virtual machine direct access to a physical hard drive on your host computer — using the disk type referred to as a physical disk.

A virtual disk is a file or set of files that appears as a physical disk drive to a guest operating system. The files can be on the host machine or on a remote computer. When you configure a virtual machine with a virtual disk, you can install a new operating system onto the virtual disk without repartitioning a physical disk or rebooting the host.

IDE virtual disks can be as large as 128GB. SCSI virtual disks can be as large as 256GB. Depending on the size of the virtual disk and the host operating system, GSX Server creates one or more files to hold each virtual disk.

By default, the virtual disk is configured so all the disk space is allocated at the time the virtual disk is created. This type of virtual disk is known as a preallocated disk. A preallocated disk provides enhanced performance and is useful if you are running performance-sensitive applications in the virtual machine. Virtual disks created in this way are similar to the experimental plain disks that could be created under earlier versions of GSX Server.

A virtual disk that is not preallocated is known as a growable disk.

You can configure the virtual disk so its actual files start out small and grow to their maximum size as needed. The main advantage of this approach is the smaller file size. Smaller files require less storage space and are easier to move if you want to move the virtual machine to a new location. You can shrink this type of virtual disk. However, it takes longer to write data to a disk configured in this way.

Virtual disks can be set up as IDE disks for any guest operating system. They can be set up as SCSI disks for any guest operating system that has a driver for the BusLogic SCSI adapter used in a GSX Server virtual machine.

A virtual disk of either type can be stored on either type of physical hard disk. That is, the files that make up an IDE virtual disk can be stored on either an IDE hard disk or a SCSI hard disk. So can the files that make up a SCSI virtual disk. They can also be stored on other types of fast-access storage media, such as DVD-ROM or CD-ROM discs. For information about running virtual machines from DVD-ROM or CD-ROM, see Running Virtual Machines from DVD-ROM or CD-ROM Discs.

A key advantage of virtual disks is their portability. Because the virtual disks are stored as files on the host machine or a remote computer, you can move them easily to a new location on the same computer or to a different computer. You can also use GSX Server on a Windows host to create virtual disks, then move them to a Linux computer and use them under GSX Server for Linux — or vice versa. For information about moving virtual disks, see Moving and Sharing Virtual Machines.

A physical disk directly accesses an existing local disk or partition. You can use physical disks if you want GSX Server to run one or more guest operating systems from existing disk partitions. Physical disks may be set up on both IDE and SCSI devices. At this time, however, booting from an operating system already set up on an existing SCSI disk or partition is not supported.

The most common use of a physical disk is to convert a dual-boot or multiple-boot machine so one or more of the existing operating systems can be run inside a virtual machine.

Physical disks may be set up on both IDE and SCSI devices. Physical disks can be as large as 128GB when configured as IDE or 256GB when configured as SCSI.

You can create a new virtual machine that uses a physical disk instead of a virtual disk. For details, see Installing an Operating System onto a Physical Partition from a Virtual Machine. In most cases, however, it is better to use a virtual disk.

Only advanced users should attempt physical disk configurations.

In older VMware products, physical disks were called raw disks.

Independent disks add a layer of control and complexity to your virtual disks. You configure virtual disks in independent mode for certain special purpose configurations.

For example, you may want to run a virtual machine that uses a virtual disk stored on DVD-ROM or CD-ROM. For more information, see Running Virtual Machines from DVD-ROM or CD-ROM Discs.

Or, you may want to exclude one or more virtual disks from a virtual machine's snapshot. For more information about snapshots, see Taking Snapshots.

To configure a disk as an independent disk, choose VM > Settings, select the virtual disk in question, then click Advanced. On the advanced settings screen, select Independent, then the mode for the disk. You have the following options for an independent disk: