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Service
DLMFS
13.1.3 Disk Heartbeat
OCFS2 requires the nodes to be alive on the network. The O2CB cluster service sends
regular keepalive packets to ensure that they are. It uses a private interconnect between
nodes instead of the LAN to avoid network delays that might be interpreted as a node
disappearing and thus, lead to a node's self-fencing.
The OC2B cluster service communicates the node status via a disk heartbeat. The
heartbeat system file resides on the 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).
13.1.4 In-Memory File Systems
OCFS2 uses two in-memory file systems for communications:
270
Installation and Administration
Description
User space interface to the kernel space DLM. For de-
tails, see
Section 13.1.4, "In-Memory File Systems"
(page 270).
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Troubleshooting
