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A simple approach to the OCFS2 cluster filesystem
Divide and Conquer
Wherever two or more computers need to access the same set of data, Linux and Unix systems will have multiple competing approaches. (For an overview of the various technologies, see the "Shared Filesystems" box.) In this article, I take a close look at OCFS2, the Oracle Cluster File System shared disk filesystem [1]. As the name suggests, this filesystem is mainly suitable for cluster setups with multiple servers.
Shared Filesystems
The shared filesystem family is a fairly colorful bunch. By definition, they all share the ability to grant multiple computers simultaneous access to certain data. The differences are in the way they implement these requirements.
On the one hand are network filesystems, in which the most popular representative in the Unix/Linux camp is Network Filesystem (NFS) [2]. NFS is available for more or less any operating system and to all intents and purposes only asks the operating system to provide a TCP/IP stack. The setup is also fairly simple. The Andrew filesystem (AFS) is another network filesystem that is available in a free implementation, OpenAFS [3].
On the other hand are cluster filesystems. Before computers can access "distributed" data, they first need to enter the cluster. The cluster setup requires additional infrastructure, such as additional I/O cards, cluster software, and, of course, a configuration. Cluster filesystems are also categorized by the way they store data. Those based on shared disks allow multiple computers to read and write to the same medium. I/O is handled via Fibre Channel ("classical SAN") or TCP/IP (iSCSI). The most popular representatives in the Linux camp here are OCFS2 and
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