Dynamic I/O Reconfiguration for a NFS-Based Parallel File System

The large gap between the speed in which data can be processed and the performance of I/O devices makes the shared storage infrastructure of a cluster a great bottle-neck. Parallel File Systems try to smooth such difference by distributing data onto several servers, increasing the system's available bandwidth. However, most implementations use a fixed number of I/O servers, defined during the initialization of the system, and can not add new resources without a complete redistribution of the existing data. With the execution of different applications at the same time, the concurrent access to these resources can aggravate the existing bottleneck, making very hard to define an initial number of servers that satisfies the performance requirements of different applications. This paper presents a reconfiguration mechanism for the dNFSp file system that uses on-line monitoring of application's I/O behavior to detect performance contention and dedicate more I/O resources to applications with higher demands. These extra resources are taken from the available nodes of the cluster, using their I/O devices as a temporary storage. We show that this strategy is capable of increasing the I/O performance in up to 200% for access patterns with short I/O phases and 47% for longer I/O phases.