VMware GSX Server 2.5.2Features | Documentation | Knowledge Base | Discussion Forums In the most common configurations, GSX Server creates virtual hard disks (or virtual 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 known as a raw disk. Or you can choose to allocate all the space a virtual disk when you create it, which creates a type of virtual disk called a plain disk. For all disk types, the size of the disk can be as large as 128GB if configured as IDE or 256GB if configured as SCSI. The disk files for a virtual disk store the information that you write to a virtual machine's hard disk — the operating system, the program files and the data files. The virtual disk files have a .vmdk extension. 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. Virtual disks can be as large as 128GB when configured as IDE or 256GB when configured as SCSI. GSX Server creates a file for each 2GB of virtual disk capacity and virtual machine overhead. The actual files used by the virtual disk start out small and grow to their maximum size as needed. However, you can choose to allocate all the disk space when you create the virtual machine. This provides better performance, but you must have the disk space available on your host when you create the virtual machine. 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. Note: To use SCSI disks in a Windows XP or Windows Server 2003 virtual machine, you need a special SCSI driver available from the download section of the VMware Web site at www.vmware.com/download. Follow the instructions on the Web site to use the driver with a fresh installation of Windows XP or Windows Server 2003. 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 backed up 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 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. Note: Beginning with GSX Server 2, virtual disks are created in a new format that is not recognized by earlier VMware products except for VMware Workstation 3.0 and later. Future versions of other VMware products will support this new virtual disk format. GSX Server 2 supports virtual disks created in the old format; to convert these disks to the new format, shrink the virtual disks. For more information, see Defragmenting and Shrinking Virtual Disks. A raw disk directly accesses an existing local disk or partition. You can use raw disks if you want GSX Server to run one or more guest operating systems from existing disk partitions. 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 raw disk is for converting a dual-boot or multiple-boot machine so one or more of the existing operating systems can be run inside a virtual machine. Raw disks may be set up on both IDE and SCSI devices. Raw disks can be as large as 128GB when configured as IDE or 256GB when configured as SCSI. Caution: If you run an operating system natively on the host computer, then switch to running it inside a virtual machine, the change is like pulling the hard drive out of one computer and installing it in a second computer with a different motherboard and other hardware. You need to prepare carefully for such a switch. The specific steps you need to take depend on the operating system you want to use inside the virtual machine. For details, see Configuring a Dual-Boot Computer for Use with a Virtual Machine. You can create a new virtual machine using a raw disk. For details, see Installing an Operating System onto a Raw Partition from a Virtual Machine. In most cases, however, it is better to use a virtual disk. Only expert users should attempt raw disk configurations. A plain disk is a type of virtual disk that provides another way to create large disks for the virtual machine. The difference is that, for a plain disk, the full capacity of the disk is allocated when you create the disk, provided the space is available on the host. Plain disks can be as large as 128GB. Virtual disks with their disk space pre-allocated perform better and you can install the guest operating system faster. A plain disk is useful for clustering virtual machines. For more information about clustering, see High-Availability Configurations with GSX Server. Virtual machines with plain disks created in GSX Server 1 run under GSX Server 2. |
