In many ways SCSI and IDE support for virtual disks and CD-ROM or DVD-ROM devices are equivalent. SCSI virtual disks may be backed either by disk files or by raw device access. SCSI virtual disks may be used in persistent, nonpersistent and undoable modes. A SCSI CD-ROM drive is always associated with a physical device — either an ATAPI or a SCSI unit.
One improvement that VMware GSX Server's SCSI implementation offers compared to its IDE implementation is that the SCSI implementation can have larger disks (up to 256GB) and as many as seven devices. IDE supports only 128GB and four devices. Further, there are no restrictions on the set of devices that may be configured on a SCSI adapter; that is, there are no master/slave requirements like there are for IDE. Finally, the operating system overhead for accessing SCSI devices is typically less than for IDE, which can translate into higher overall performance for SCSI devices.
The downside to using SCSI is that operating system support sometimes is not present or requires additional configuration, which can be involved.
The other potential difficulty with using SCSI is that the BIOS in some machines does not include support for booting from SCSI devices. To address this issue, the normal VMware GSX Server BIOS has been augmented to support booting from SCSI disk devices.
Note: You cannot boot from a virtual SCSI CD-ROM device. If you have a physical SCSI CD-ROM, configure a virtual IDE CD-ROM device for it, and you can then boot from that virtual device.
© 2001-2002 VMware, Inc. All rights reserved.