Red Hat CLUSTER FOR ENTERPRISE LINUX 5.0, Configuration Manual

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Important
Overall, heuristics and other
qdiskd
parameters for your Red Hat Cluster
depend on the site environment and special requirements needed. To
understand the use of heuristics and other
qdiskd
parameters, refer to the
qdisk(5) man page. If you require assistance understanding and using
qdiskd
for
your site, contact an authorized Red Hat support representative.
If you need to use
qdiskd
, you should take into account the following considerations:
Cluster node votes
Each cluster node should have the same number of votes.
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.
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