Red Hat ENTERPRISE LINUX 4 - ADMINISTRATION Manual

Also see for ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE: Installation guide Installation guide Tuning guide Installation guide Manual

Contents

Red Hat Cluster Suite and SELinux21qdiskd membership timeout value. The reason is because the quorum daemon must detectfailed nodes on its own, and can take much longer to do so than CMAN. The default valuefor CMAN membership timeout is 10 seconds. Other site-specific conditions may affect therelationship between the membership timeout values of CMAN and qdiskd. For assistancewith adjusting the CMAN membership timeout value, contact an authorized Red Hat supportrepresentative.FencingTo 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 reliablefor clusters not configured with qdiskd, they are not reliable for a cluster configured with qdiskd.Maximum nodesA cluster configured with qdiskd supports a maximum of 16 nodes. The reason for the limitis because of scalability; increasing the node count increases the amount of synchronous I/Ocontention on the shared quorum disk device.Quorum disk deviceA quorum disk device should be a shared block device with concurrent read/write access byall nodes in a cluster. The minimum size of the block device is 10 Megabytes. Examples ofshared block devices that can be used by qdiskd are a multi-port SCSI RAID array, a FibreChannel RAID SAN, or a RAID-configured iSCSI target. You can create a quorum disk devicewith mkqdisk, the Cluster Quorum Disk Utility. For information about using the utility refer to themkqdisk(8) man page.NoteUsing JBOD as a quorum disk is not recommended. A JBOD cannot providedependable performance and therefore may not allow a node to write to it quicklyenough. If a node is unable to write to a quorum disk device quickly enough, the nodeis falsely evicted from a cluster.2.6. Red Hat Cluster Suite and SELinuxRed Hat Cluster Suite for Red Hat Enterprise Linux 4 requires that SELinux be disabled. Beforeconfiguring a Red Hat cluster, make sure to disable SELinux. For example, you can disable SELinuxupon installation of Red Hat Enterprise Linux 4 or you can specify SELINUX=disabled in the /etc/selinux/config file.2.7. Considerations for Using CongaWhen using Conga to configure and manage your Red Hat Cluster, make sure that each computerrunning luci (the Conga user interface server) is running on the same network that the cluster is usingfor cluster communication. Otherwise, luci cannot configure the nodes to communicate on the rightnetwork. If the computer running luci is on another network (for example, a public network ratherthan a private network that the cluster is communicating on), contact an authorized Red Hat supportrepresentative to make sure that the appropriate host name is configured for each cluster node.