In-Memory File Systems - Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual

The OC2B cluster service communicates the node status via a disk heartbeat. The
heartbeat system file resides on the Storage Area Network (SAN), where it is available
to all nodes in the cluster. The block assignments in the file correspond sequentially to
each node's slot assignment.
Each node reads the file and writes to its assigned block in the file at two-second inter-
vals. Changes to a node's time stamp indicates the node is alive. A node is dead if it
does not write to the heartbeat file for a specified number of sequential intervals, called
the heartbeat threshold. Even if only a single node is alive, the O2CB cluster service
must perform this check, because another node could be added dynamically at any time.
You can modify the disk heartbeat threshold in the /etc/sysconfig/o2cb file,
using the O2CB_HEARTBEAT_THRESHOLD parameter. The wait time is calculated
as follows:
(O2CB_HEARTBEAT_THRESHOLD value - 1) * 2 = threshold in seconds
For example, if the O2CB_HEARTBEAT_THRESHOLD value is set at the default value
of 7, the wait time is 12 seconds ((7 - 1) * 2 = 12).

14.3 In-Memory File Systems

OCFS2 uses two in-memory file systems for communications:
Table 14.2
In-Memory
File System
configfs
ocfs2_dlmfs
292 Installation and Administration
In-Memory File Systems Used by OCFS2
Description
Communicates the list of nodes in the cluster to
the in-kernel node manager, and communicates the
resource used for the heartbeat to the in-kernel
heartbeat thread
Communicates locking and unlocking for cluster-
wide locks on resources to the in-kernel distributed
lock manager that keeps track of all locks and their
owners and status
Mount Point
/config
/dlm