• How RAM disk cluster resources are implemented
• The RAM disk's size and drive letter,
• The impact of reduced available system memory on the cluster application,
• On a production cluster, a convenient time when the cluster application can be stopped

SuperSpeed's RAM disk cluster resource implementation creates the illusion of a single RAM disk being shared by all nodes in the cluster. As indicated above, a cluster application running on a given node can only access a local RAM disk configured as a cluster resource. However, if each node has its own local RAM disk, a given node's RAM disk can be made available to dependent resources when that node becomes active.

In SuperSpeed's cluster resource implementation, a RAM disk must exist on each node in the cluster. Each RAM disk should be the same size and must use the same drive letter. When a group containing a RAM Disk cluster resource is brought online, the RAM disk local to the node becomes accessible to its dependent applications or resources, also running on the node. When the group is moved to a second node, the RAM disk on the second node becomes accessible to the applications or resources running on that node.

From the above it is clear that whatever has been stored on one node's RAM disk, will not be available on a different node. The RAM Disk cluster resource can only be used by applications or resources that do not require data persistence when moving the resource from one node to another. An ideal candidate for a RAM Disk cluster resource are the tempdb files of SQL Server. These files are re-created each time SQL server starts up. Frequently, they are also the cause of a performance bottleneck which can be eliminated by locating the files on a RAM disk.

The drive letter to be assigned to the RAM disk must be unassigned on all cluster nodes. Make sure it is not assigned to a network drive, which some tools may display as unassigned.

However, over-allocation of memory resources to the RAM disk can result in a lower overall performance. Frequently, it is necessary to experiment with different allocation sizes to find the best balance and optimize performance.

Most cluster applications' configuration settings include limits on memory resource allocations. These settings may have to be reduced to free system memory for the RAM disk's allocation. In order to take effect, the application must be stopped to free its resources, the configuration setting changed, and the application restarted afterwards.

Additionally, to take advantage of the RAM Disk cluster resource, the application must be reconfigured to place its temporary data on the RAM disk. Once again, this change requires that the application be stopped, reconfigured, and restarted.