ADMIN

OCFS2
Tools
ing. OCFS2 is fairly simplistic in its
approach and only uses self-fencing.
If a node notices that it is no longer
cleanly integrated with the cluster, it
throws a kernel panic and locks itself
out. Just like the DLM, self-fencing
in OCFS2 does not require a separate
configuration. Once the cluster configuration
is complete and has been
distributed to all the nodes, the brunt
of the work has been done for a functional
OCFS2.
Things are seemingly quite simple
at this point: Start the cluster, create
OCFS2 if needed, mount the filesystem,
and you’re done.
Getting Started
As I mentioned earlier, OCFS2 is a
cluster filesystem based on shared
disks. The range of technologies
that can provide a shared disk spans
expensive SAN over Fibre Channel,
from iSCSI to low-budget DRBD [7].
In this article, I will use iSCSI and
NDAS (Network Direct Attached Storage).
The second ingredient in the
OCFS2 setup is computers with an
OCFS2-capable operating system. The
best choices here are Oracle’s Enterprise
Linux, SUSE Linux Enterprise
Server, openSUSE, Red Hat Enterprise
Linux, and Fedora.
The software suite for OCFS2 comprises
the ocfs2-tools and ocfs2console
packages and the ocfs2‐`uname
‐r` kernel modules. Typing ocfs2console
launches a graphical interface in
which you can create the cluster configuration
and distribute it over the
nodes involved (Figure 1). However,
you can just as easily do this with vi
and scp. Table 1 lists the actions the
graphical front end supports and the
equivalent command-line tools.
After creating the cluster configuration,
/etc/init.d/o2cb online
launches the subsystem (Listing 2).
The init script loads the kernel modules
and sets a couple of defaults for
the heartbeat and fencing.
Once the OCFS2 framework is running,
the administrator can create
the cluster filesystem. In the simplest
case, you can use mkfs.ocfs2
devicefile (Listing 3) to do this. The
Figure 1: Cluster configuration with the ocfs2console GUI tool.
man page for mkfs.ocfs provides a
full list of options, the most important
of which are covered by Table 2.
Once you have created the filesystem,
you need to mount it. The mount
command works much like that on
unclustered filesystems (Figure 2).
When mounting and unmounting
Option
b
C
L
N
J
T
Table 1: Directories in a Repository
Table 2: Important Options for mkfs.ocfs2
Purpose
Block size
Cluster size
Label
OCFS2 volumes, you can expect a
short delay: During mounting, the
executing machine needs to register
with the DLM. In a similar fashion,
the DLM resolves any existing locks
or manages them on the remaining
systems in case of a umount. The documentation
points to various options
Filesystem Function GUI Menu CLI Tool
Mount Mount mount.ocfs2
Unmount Unmount umount
Create Format mkfs.ocfs2
Repair Check fsck.ocfs2
Repair Repair fsck.ocfs2
Change name Change Label tunefs.ocfs2
Maximum number of nodes Edit Node Slot Count tunefs.ocfs2
node:
node:
Maximum number of computers with simultaneous access
Journal options
Filesystem type (optimization for many small files or a few large ones)
Listing 1: /etc/​ocfs2/​cluster.conf
ip_port = 7777
ip_address = 192.168.0.1
number = 0
name = node0
cluster = ocfs2
ip_port = 7777
ip_address = 192.168.0.2
number = 1
name = node1
cluster = ocfs2
cluster:
node_count = 2
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