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A simple approach to the OCFS2 cluster filesystem
Divide and Conquer
The vanilla kernel includes two cluster filesystems: OCFS2 has been around since 2.6.16 and is thus senior to
GFS2. Although OCFS2 is non-trivial under the hood, it is fairly simple to deploy. By Udo Seidel
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.
Before you can set up a cluster filesystem
based on shared disks, you
need to look out for a couple of
things. First, the administrator needs
to establish the basic framework of a
cluster, including stipulating the computers
that belong to the cluster, how
to access it via TCP/​IP, and the cluster
name. In OCFS2’s case, a single
ASCII file is all it takes (Listing 1).
The second task to tackle with a cluster
filesystem is that of controlled and
orderly access to the data with the
use of file locking to avoid conflict situations.
In OCFS2’s case, the Distributed
Lock Manager (DLM) prevents
filesystem inconsistencies. Initializing
the OCFS2 cluster automatically
launches DLM, so you don’t need to
configure this separately. However,
the best file locking is worthless if the
computer writing to the filesystem
goes haywire. The only way to prevent
computers from writing is fenc-
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