Installation guide

CMAN membership timeout value

The CMAN membership timeout value (the time a node needs to be unresponsive before

CMAN considers that node to be dead, and not a member) should be at least two times that

of the qdiskd membership timeout value. The reason is because the quorum daemon must

detect failed nodes on its own, and can take much longer to do so than CMAN. The default

value for CMAN membership timeout is 10 seconds. Other site-specific conditions may

affect the relationship between the membership timeout values of CMAN and qdiskd. For

assistance with adjusting the CMAN membership timeout value, contact an authorized Red

Hat support representative.

Fencing

To ensure reliable fencing when using qdiskd, use power fencing. While other types of

fencing (such as watchdog timers and software-based solutions to reboot a node internally)

can be reliable for clusters not configured with qdiskd, they are not reliable for a cluster

configured with qdiskd.

Maximum nodes

A cluster configured with qdiskd supports a maximum of 16 nodes. The reason for the limit

is because of scalability; increasing the node count increases the amount of synchronous

I/O contention on the shared quorum disk device.

Quorum disk device

A quorum disk device should be a shared block device with concurrent read/write access by

all nodes in a cluster. The minimum size of the block device is 10 Megabytes. Examples of

shared block devices that can be used by qdiskd are a multi-port SCSI RAID array, a Fibre

Channel RAID SAN, or a RAID-configured iSCSI target. You can create a quorum disk

device with mkqdisk, the Cluster Quorum Disk Utility. For information about using the utility

refer to the mkqdisk(8) man page.

Note

Using JBOD as a quorum disk is not recommended. A JBOD cannot provide

dependable performance and therefore may not allow a node to write to it quickly

enough. If a node is unable to write to a quorum disk device quickly enough, the

node is falsely evicted from a cluster.

7. Multicast Addresses

Red Hat Cluster nodes communicate among each other using multicast addresses. Therefore,

each network switch and associated networking equipment in a Red Hat Cluster must be

configured to enable multicast addresses and support IGMP (Internet Group Management

Protocol). Ensure that each network switch and associated networking equipment in a Red Hat

Cluster are capable of supporting multicast addresses and IGMP; if they are, ensure that

Chapter 2. Before Configuring a Red Hat Cluster