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Cluster Customization 125
The failure rate of networks varies, depending on their characteristics. For
example, for an Ethernet, the normal failure detection rate is two keepalives
per second; fast is about four per second; slow is about one per second. For
an HPS network, because no network traffic is allowed when a node joins the
cluster, normal failure detection is 30 seconds; fast is 10 seconds; slow is 60
seconds.
The Change / Show Topology and Group Services Configuration screen
includes the settings for the length of the Topology and Group services logs.
The default settings are highly recommended. The screen also contains
entries for heartbeat settings, but these are not operable (see
HACMP/ES
Installation and Administration Guide
, SC23-4284, Chapter 18). The
heartbeat rate is now set for each network module in the corresponding
screen (see above).
To learn more about Topology and Group Services, see Chapter 32 of the
HACMP/ES Installation and Administration Guide
, SC23-4284.
5.4 NFS considerations
For NFS to work correctly in an HACMP cluster environment, you have to
take care of some special NFS characteristics.
The HACMP scripts have only minimal NFS support. You may need to modify
them to handle your particular configuration. The following sections contain
some suggestions for handling a variety of issues.
5.4.1 Creating Shared Volume Groups
When creating shared volume groups, normally, you can leave the Major
Number field blank and let the system provide a default for you. However,
unless all nodes in your cluster are identically configured, you will have
problems using NFS in an HACMP environment. The reason is that the
system uses the major number as part of the file handle to uniquely identify a
Network File System.
In the event of node failure, NFS clients attached to an HACMP cluster
operate exactly the way they do when a standard NFS server fails and
reboots. If the major numbers are not the same, when another cluster node
takes over the file system and re-exports it, the client application will not
recover, since the file system exported by the node will appear to be different
from the one exported by the failed node.