Sun Microsystems 3.0.0 user manual

5 Virtual storage

CD-ROM/DVD drive, this leaves you with up to three virtual hard disks that you can attach to a virtual machine’s IDE controller.

So even if your guest operating system has no support for SCSI or SATA devices, it should always be able to see the default IDE controller that is enabled by default. Of the four slots attached to it, one is normally used when you create a virtual machine with the “New Virtual Machine” wizard of the graphical user interface.

•SCSI is another established industry standard, standing for “Small Computer System Interface”. This was established as early as 1986 as a generic interface for data transfer between all kinds of devices, including storage devices. Today SCSI is still used for connecting hard disks and tape devices, but it has mostly been displaced in commodity hardware. It is still in common use in high-performance workstations and servers.

Primarily for compatibility with other virtualization software, VirtualBox option- ally supports LsiLogic and BusLogic SCSI controllers, to which up to 16 virtual hard disks can be attached.

To enable the SCSI controller, on the “Hard Disks” page of a virtual machine’s settings dialog, check the “Enable Additional Controller” box and select one of the two SCSI modes from the list below. After this, the additional controller will appear as a separate PCI device in the virtual machine.

Warning: There are limitations with the default SCSI drivers shipped with

some operating systems: the standard Windows XP driver for the LsiLogic controller does not detect a hard disk attached to the controller’s first port, and the BusLogic controller does not work with Windows NT4 guests.

•Finally, Serial ATA (SATA) is a newer standard introduced in 2003. Compared to IDE, it supports both much higher speeds and more devices per hard disk con- troller. Also, with real hardware, devices can be added and removed while the system is running. The standard interface for SATA controllers is called Advanced Host Controller Interface (AHCI).

For compatibility reasons, AHCI controllers by default operate the disks attached to it in a so-called IDE compatibility mode, unless SATA support is explicitly requested. “IDE compatibility mode” means that the BIOS can operate these drives. Disks assigned to those slots will operate in full-speed AHCI mode once the guest operating system has loaded its AHCI device driver.

Like a real SATA controller, VirtualBox’s virtual SATA controller operates faster and also consumes less CPU resources than the virtual IDE controller. Also, this allows you to connect up to 30 virtual hard disks to one machine instead of just three, as with IDE. Of these, the first four (numbered 0-3 in the graphical user interface) are operated in IDE compatibility mode by default.

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