Cluster Service Features in Windows Server 2003

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

The Windows Server 2003 release has a number of enhancements. The following enhancements are specific to supporting Server clusters in a SAN environment:

Targeted Reset

Historically, server clusters use the SCSI reservation mechanism to protect disks against access, guaranteeing that only the host that has the disk online can actually access it. To ensure that devices can be failed over in the event of failures, server clusters implements a challenge/response mechanism that can detect dead or unresponsive server nodes even though they may not have crashed and therefore the storage fabric is unaware that the server is not responding. To do this, the reservations are periodically broken by other nodes in the cluster using SCSI bus reset commands. In a SAN fabric, SCSI reset commands can be very detrimental to the fabric since they are typically not implemented the same way by different vendors and they typically result in a LIP command that takes the fabric sometime to re-settle.

In Windows Server 2003, the server cluster code uses a new mechanism to first try targeted device reset, then LUN reset and if all else fails it will fall-back to a full bus reset. This feature requires the storage mini-port drivers to interpret the new control codes. At this time, several HBA vendors are modifying their mini-port drivers to provide this feature, thus enabling much more stable cluster configurations in a switched fabric environment.

This feature requires no administration to enable it. If the device driver supports the targeted reset functions they will be automatically used.

Single Storage Bus Configurations

As described previously, in Windows 2000, only storage devices on a different bus to the system disk will be considered eligible as cluster-managed devices. In a SAN environment, the goal is to centralize all storage into a single fabric accessible through a single port (actually in most cases the host will have multiple HBAs and multi-path drivers to provide a single port view to the cluster software).

In Windows Server 2003 Cluster server has a switch that when enabled, allows any disk on the system, regardless of the bus it is on, to be eligible as a cluster-managed disk. Using this, the system disk, startup disk, pagefile disks and any cluster managed disks can be attached to the same HBA. This feature is enabled by setting the following registry key:

HKLM\SYSTEM\CurrentControlSet\Services\ClusSvc\Parameters\ManageDisks 
OnSystemBuses   0x01 

This feature is enabled by a registry key to ensure that it is not accidentally enabled by customers that do not understand the implications of this configuration. It is intended for OEMs to ship qualified and tested configurations and not for a typical end-user or administrator to setup in an ad hoc manner.

A single storage bus configuration MUST have device drivers that support the targeted reset functionality previously defined.