3.7.2 Changing the maximum number of hosts
The default for the maximum number of hosts in a hot-standby configuration is 32. When you use HA Monitor Extension, you can increase this number to more than 32, which enables you to apply one hot-standby configuration to a large system in which more than 32 hosts run concurrently.
- Organization of this subsection
(1) Maximum number of hosts that can be specified
When you use HA Monitor Extension, you can specify any value from 32 to 256 as the maximum number of hosts in a hot-standby configuration.
(2) Operation when the maximum number of hosts is set to more than 32
When the maximum number of hosts is set to more than 32, alive messages are transmitted by multicasting on all monitoring paths. When one alive message is sent by multicasting, all HA Monitors (other than the local HA Monitor) receive the alive message. For details about alive messages, see (1) Monitoring between hosts.
(3) Required environment settings
To change the maximum number of hosts, you must specify the following environment settings:
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Specify the maximum number of hosts in a single hot-standby configuration in the hostmax operand in the HA Monitor environment settings.
If the hot-standby configuration contains any host whose maximum count has been increased, you must specify this operand on all hosts in the hot-standby configuration.
Note that when you set the maximum number of hosts to more than 32, the alive message communication method is set automatically to multicasting. You can also use the alive_multicast operand in the HA Monitor environment settings to specify the multicast communication method.
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If you want to specify a desired multicast group ID, specify it and the host name corresponding to that multicast group ID in the /etc/hosts file. You must also specify the host name that you specified in the /etc/hosts file in the multicast_lan operand in the HA Monitor environment settings.
If the multicast_lan operand is omitted, 239.0.0.1 will be assumed as the multicast group ID.
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Execute the HA Monitor environment setup command (monsetup -ex command) to enable the functions of HA Monitor Extension.
The following figure shows an example of the environment settings for changing the maximum number of hosts.
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![[Figure]](GRAPHICS/F0000085.GIF)
This example uses hosts 1 through 32 as primary systems and host 33 as the secondary system. For hosts 1 through 32, the number of hosts to be connected is 2 including the local host because they all connect to host 33. For host 33, the number of hosts to be connected is 33 including the local host because host 33 connects to hosts 1 through 32. Therefore, for host 33, 33 is specified in the hostmax operand. For hosts 1 through 32, although the number of hosts to be connected is 2 for each of them, 33 is specified in the hostmax operand because each of these hosts connects to host 33 for which the maximum number of hosts is set to 33 or greater.