Installation guide

Important
Overall, heuristics and other q d i skd parameters for your deployment depend on the site
environment and special requirements needed. To understand the use of heuristics and other
q d i skd parameters, refer to the qdisk(5) man page. If you require assistance understanding
and using q d i skd for your site, contact an authorized Red Hat support representative.
If you need to use q d i skd , you should take into account the following considerations:
Clu st er n o d e vo t es
When using Quorum Disk, each cluster node must have one vote.
CMAN memb ersh ip t imeo u t valu e
The q d i skd membership timeout value is automatically configured based on 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). q d i skd also performs extra sanity
checks to guarantee that it can operate within the CMAN timeout. If you find that you need to
reset this value, you must take the following into account:
The CMAN membership timeout value should be at least two times that of the q d i skd
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. Other site-specific
conditions may affect the relationship between the membership timeout values of CMAN and
q d i skd . For assistance with adjusting the CMAN membership timeout value, contact an
authorized Red Hat support representative.
Fen cin g
To ensure reliable fencing when using q d i skd , use power fencing. While other types of
fencing can be reliable for clusters not configured with q d i skd , they are not reliable for a
cluster configured with q d i skd .
Maximum no d es
A cluster configured with q d i skd 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.
Q u o ru m disk d evice
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 q d i skd 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 mkq d i sk, the Cluster Quorum Disk Utility. For information about using the
utility refer to the mkqdisk(8) man page.
⁠Chapt er 2 . Before Configuring t he Red Hat High Availabilit y Add- O n
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