Parallel I/O Traffic

Sun MPI programs can make use of the parallel I/O capabilities of Sun HPC ClusterTools, but not all such programs will do so. The administrator needs to understand how distributed multiprocess applications that are run on the Sun HPC cluster will make use of parallel I/O to understand the ramifications for network load.

Applications can use parallel I/O in two different ways, and the choice is made by the application developer. Applications that use parallel I/O to read from and write to standard UNIX file systems can generate NFS traffic on the default network, on the network being used by the Sun MPI component, or some combination of the two. The type of traffic that is generated depends on the type of I/O operations being used by the applications. Collective I/O operations will generate traffic on the Sun MPI network, while most other types of I/O operations will involve only the default network.

Applications that use parallel I/O to read from and write to PFS file systems will use the network specified by the CRE. In a one-network cluster, this means that parallel I/O traffic will be routed over the same network used by all other internode traffic. In a two-network cluster, where an additional network has been established for use by parallel applications, the administrator would normally configure the CRE so that this type of parallel I/O would be routed over the parallel application network. A Sun HPC cluster can be configured to allow parallel I/O traffic to be routed by itself over a dedicated third network if that amount of traffic segregation is desired.