Red Hat Cluster Suite And Selinux; Considerations For Using Conga - Red Hat ENTERPRISE LINUX 4 - ADMINISTRATION Manual

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.

2.6. Red Hat Cluster Suite and SELinux

Red Hat Cluster Suite for Red Hat Enterprise Linux 4 requires that SELinux be disabled. Before
configuring a Red Hat cluster, make sure to disable SELinux. For example, you can disable SELinux
upon installation of Red Hat Enterprise Linux 4 or you can specify SELINUX=disabled in the /etc/
selinux/config file.

2.7. Considerations for Using Conga

When using Conga to configure and manage your Red Hat Cluster, make sure that each computer
running luci (the Conga user interface server) is running on the same network that the cluster is using
for cluster communication. Otherwise, luci cannot configure the nodes to communicate on the right
network. If the computer running luci is on another network (for example, a public network rather
than a private network that the cluster is communicating on), contact an authorized Red Hat support
representative to make sure that the appropriate host name is configured for each cluster node.
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