Support for parallel SCSI as a shared bus type has been removed in Windows Server 2008 Failover Clusters. Serial Attached SCSI (SAS) is the next evolution of parallel SCSI. SAS is replacing parallel SCSI as a simple and low-cost cluster solution. Most vendors have SAS-based cluster solutions that are available today.
A trend in the storage industry is to phase out existing parallel SCSI devices and to replace them with newer SAS solutions. It is estimated that by the year 2010, SCSI devices will no longer be shipped. Therefore, parallel SCSI technology will not be around for the lifespan of Windows Server 2008.
Parallel SCSI has many limitations that make it less than optimal as a shared bus. For example, issues with termination, cable length, and units of failover are common. Additionally, parallel SCSI does not support SPC-3 Persistent Reservations (PRs). SPC-3 PRs are a requirement for Windows Server 2008 storage solutions. SAS delivers superior I/O performance and compatibility for a comparable price. Storage vendors are not making any future investments in parallel SCSI, and the storage vendors are moving to SAS technologies as the replacement for parallel SCSI.
Windows Server 2008 Failover Clusters support the following types of storage connections:
Effects on virtualization
The deprecation of parallel SCSI support in Windows Server 2008 also affects the configuration of virtual computers. Parallel SCSI storage is no longer available to be used in a virtual environment for failover clustering. When you configure a Windows Server 2008 Failover Cluster in a virtual environment, the only option for storage is an iSCSI solution.
Important Microsoft supports a failover cluster solution only if all the hardware components are marked as "Certified for Windows Server 2008." In addition, the complete configuration (The complete configuration includes servers, network, and storage.) must pass all tests in the Validate a Configuration Wizard. This wizard is included in the Failover Cluster Management snap-in.
For more information, visit the following Failover Clustering Configuration Program Web site: