1. A method for optimizing a file system for different types of applications in a compute cluster using dynamic block size granularity, comprising: reserving a predetermined number of storage allocation regions for each node in a cluster, wherein each storage allocation region comprises a set of contiguous data blocks on a single storage disk of locally attached storage; using a contiguous set of data blocks on a single storage disk of locally attached storage as a file system's block allocation granularity for striping data to be stored in the file system for a compute operation in the cluster; and using a single data block of a shared storage subsystem as the file system's block allocation granularity for striping data to be stored in the file system for a data access operation in the cluster.