Understanding and Configuring VirtualBox Virtual Hard Disks

Most operating systems require access to some form of storage space, typically in the form of a disk drive, to store operating system files and user data. The guest operating systems supported by VirtualBox are no exception to this rule and to meet this requirement, VirtualBox provides a number of virtual hard disk drive configuration options, each of which is the topic of this chapter.

VirtualBox provides access to storage by presenting virtual hard disk controllers to virtual machines. Although controllers are essentially software emulations of hard disk controllers, as far as the guest operating systems are concerned, these appear as real, physical devices. A number of different standards of disk controller have developed over the years and VirtualBox provides virtual versions of the following standards:

• Serial ATA (SATA/AHCI) - The latest drive controller standard, SATA provides higher levels of storage access performance and, unlike the older IDE standard, does not impose restrictions on the number of devices that can be attached to a single disk controller. VirtualBoix allows up to 30 SATA slots to be configured. The first 4 of these are configured to operating in IDE compatibility mode, which allowing them to be accessed by guest operating systems which lack support for the Advanced Host Controller Interface (AHCI).

• Integrated Drive Electronics (IDE) - Perhaps the most widely used disk controller standard, these controllers are now being replaced in favor of the SATA standard. The VirtualBox virtual IDE disk controller allows up to four storage devices to be connected to a virtual machine. The secondary master connection is reserved for CD/DVD devices, allowing for the attachment of three virtual hard disks to the controller.

• Small System Computer Interface (SCSI) - A popular storage connection standard, SCSI is based on a bus topology allowing up to 16 stroage devices to be conncted to a disk controller in a daisy chain configuration. Each device is assigned a unique SCSI identifier to distinguish it from other devices on the SCSI bus. VirtualBox provides emulation for BusLogic and LsiLogic 53c1030 SCSI disk controllers.