This parameter, which enables HADR to run in multiple standby mode, specifies a list of up to three target host:port pairs that act as HADR standby databases.
For HADR to run in multiple standby mode, you must set the hadr_target_list configuration parameter on all HADR databases. You cannot switch from single standby mode to multiple standby mode by setting this parameter without shutting down the primary. The host:port pairs that you specify for the hadr_target_list configuration parameter for a primary determine which hosts act as standbys for that primary. The host:port pairs in the target list of a standby identify the standby hosts to be used if this standby takes over as the new HADR primary database.
The default setting of NULL, indicates that HADR runs in single standby mode.
host1:port1|host2:port2|host3:port3
[FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]:4000
The first entry in the target list of an HADR database is designated as the principal HADR standby database, and any other entries are called auxiliary HADR standby databases. You can configure the principal standby database and the primary database to use any synchronization mode; however, the synchronization mode of the principal standby is determined by the setting for the hadr_syncmode configuration parameter on the primary. The synchronization mode of the auxiliary standby targets is always SUPERASYNC. When you start HADR on the primary, the values for the hadr_remote_host and hadr_remote_svc configuration parameters are automatically set to those of the principal standby unless you set the DB2_HADR_NO_IP_CHECK registry variable to ON.
There is no requirement for symmetry or reciprocal settings. For example, database A can designate database B as its principal standby, and database B can designate database C as its principal standby. However, role switch between any pair of the databases must be able to occur. For example, if database B is listed in the target list of database A, database A must be listed in the target list of database B.