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Clustered and parallel file systems: Clustered file systems operate across multiple nodes (generally more than eight) and use off-the-shelf hardware and/ or standard operating system software. The nodes can be specialized, such as meta data nodes and storage nodes, or generic, supporting both meta data and storage services. Some products mentioned in the previous sections support from two to eight NAS box clusters for high availability. However, none of the products previously mentioned does this to quite the extent available from clustered or parallel file-system products. A true clustered or parallel file system scales performance linearly as the number of nodes increases and provides access to the same data across all nodes.

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Clustered file systems are good for companies with large compute clusters that need high-performance access to file-system data. One key advantage of these products is that performance can be dialed up almost as high as you want by adding nodes to the cluster. However, these products may not be as useful for Windows users, as some have limited (or no) support for CIFS, but this is vendor-specific.

Parallel file systems are similar to clustered file systems. They provide concurrent access to a single file across a number of nodes operating in parallel. This requires file data to be striped across multiple nodes, as well as special client software to process all file parts simultaneously. Companies with large compute clusters can take advantage of the massive performance scalability inherent in these products. It's important to check which operating systems a parallel file system supports, as there may be some limitations outside of Linux.

A global name space (GNS), which provides a single mount point or share for a number of file systems, is a common feature of the non-traditional approaches to NAS consolidation. By providing a single share for a number of file systems, the GNS presents a central management point for the files under its purview. WSS and some other products can use Windows' DFS to provide a GNS across several CIFS servers.

Clustered file-system products: PolyServe Inc.'s Matrix Server software for Linux or Windows offers a clustered file system, as well as a clustered application server in one package. PolyServe clustered file-system support is NFS for the Linux Matrix Server and CIFS for the Windows Matrix Server. In addition to offering clustered file services, each Matrix Server cluster can also host applications across the cluster.

HP's Enterprise File System (EFS) gateway is based on PolyServe's Matrix Server software and supplies clustered file services to NFS clients. EFS is available in Linux and Windows versions. The Windows product supports a clustered CIFS, but has no support for NFS. The Linux product supports a clustered NFS, but a single-node CIFS. With its EFS Linux product, CIFS isn't supported as a clustered file system—not as a single namespace accessible over the whole cluster. HP said it plans to upgrade Linux EFS support for CIFS sometime this quarter. Like other cluster offerings, HP's product offers a single file namespace accessible across all cluster nodes to NFS.

This was first published in December 2005

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