Far Sync 需要初始化参数文件、密码文件、控制文件，没有数据文件。可以配置为单实例，也可以配置为RAC。
Far Sync单实例
在距离生产数据中心较近的地方建立Far Sync实例，通过SYNC的方式把Redo传输到Far Sync实例，然后通过ASYNC的方式传输到终端灾备数据库。在此过程中，如果Far Sync实例出现问题，生产数据库可以直接通过ASYNC方式把Redo传输到灾备数据库。
log_archive_dest_2='service=prodfs sync affirm max_failure=1 alternate=log_archive_dest_3 valid_for=(online_logfiles,primary_role) db_unique_name=prodfs'
log_archive_dest_3='service=stdby async noaffirm delay=0 optional compression=disable max_failure=0 max_connections=1 reopen=15 net_timeout=30 valid_for=(online_logfile,primary_role) db_unique_name=stdby'
log_archive_dest_state_3=alternate
Far Sync HA架构
可以配置两个Far Sync实例，当一个Far Sync实例出问题，另外一个可以接替
log_archive_dest_2='service=prodfs sync affirm max_failure=1 alternate=log_archive_dest_3 valid_for=(online_logfiles,primary_role) db_unique_name=prodfs'
log_archive_dest_3='service=prodfs1 sync affirm max_failure=1 alternate=log_archive_dest_2 valid_for=(online_logfiles,primary_role) db_unique_name=prodfs1'
我们还可以配置为log_archive_dest_2------->log_archive_dest_3------->log_archive_dest_4
Far Sync Role Transition
当主备库角色切换后，由于先前配置的Far Sync实例距离新的主库较远。这时，我们可以在距离新的主库较近的地方，建立新的Far Sync实例。
测试环境
测试环境为RAC + DG，配置了单实例Far Sync
配置Far Sync主要步骤为
在主库上创建far sync controlfile，pfile
alter database create far sync instance controlfile as '/tmp/controlfs01.ctl';把控制文件，密码文件，pfile传到far sync服务器
编辑pfile，启动Far Sync
SQL> startup ORACLE instance started. Total System Global Area 209715200 bytes Fixed Size 2922712 bytes Variable Size 109053736 bytes Database Buffers 92274688 bytes Redo Buffers 5464064 bytes Database mounted. ORA-16476: far sync instance does not allow Open operation SQL>
在far sync实例上创建standby logfile
alter database add standby logfile thread 1 group 7 '/pgold/oradata/sredo7.dbf' size 50m; alter database add standby logfile thread 1 group 8 '/pgold/oradata/sredo8.dbf' size 50m; alter database add standby logfile thread 1 group 9 '/pgold/oradata/sredo9.dbf' size 50m; alter database add standby logfile thread 1 group 10 '/pgold/oradata/sredo10.dbf' size 50m; alter database add standby logfile thread 2 group 11 '/pgold/oradata/sredo11.dbf' size 50m; alter database add standby logfile thread 2 group 12 '/pgold/oradata/sredo12.dbf' size 50m; alter database add standby logfile thread 2 group 13 '/pgold/oradata/sredo13.dbf' size 50m; alter database add standby logfile thread 2 group 14 '/pgold/oradata/sredo14.dbf' size 50m;
生产库信息
SQL> select instance_name from gv$instance; INSTANCE_NAME ---------------- prod1 prod2 SQL> select * from gv$dataguard_config; DB_UNIQUE_NAME PARENT_DBUN DEST_ROLE CURRENT_SCN CON_ID --------------- ------------- ----------------- ----------- ---------- prod NONE PRIMARY DATABASE 5396377 0 prodfs prod FAR SYNC INSTANCE 5333670 0 stdby prodfs PHYSICAL STANDBY 5333670 0 prod NONE PRIMARY DATABASE 5396376 0 prodfs prod FAR SYNC INSTANCE 5333670 0 stdby prodfs PHYSICAL STANDBY 5333670 0 6 rows selected. SQL>Far Sync Instance信息
SQL> select instance_name from gv$instance; INSTANCE_NAME ---------------- prodfs SQL> select * from gv$dataguard_config; DB_UNIQUE_NAME PARENT_DBUN DEST_ROLE CURRENT_SCN CON_ID -------------- ------------- ----------------- ----------- ---------- prodfs prod FAR SYNC INSTANCE 5333670 0 stdby prodfs PHYSICAL STANDBY 5333670 0 prod NONE PRIMARY DATABASE 0 0 SQL>备库信息
SQL> select instance_name from gv$instance; INSTANCE_NAME ---------------- stdby1 stdby2 SQL> select * from gv$dataguard_config; DB_UNIQUE_NAME PARENT_DBUN DEST_ROLE CURRENT_SCN CON_ID --------------- ------------- ----------------- ----------- ---------- stdby prodfs PHYSICAL STANDBY 5333670 0 prod NONE PRIMARY DATABASE 0 0 prodfs UNKNOWN FAR SYNC INSTANCE 0 0 stdby prodfs PHYSICAL STANDBY 5333670 0 prod NONE PRIMARY DATABASE 0 0 prodfs UNKNOWN FAR SYNC INSTANCE 0 0 6 rows selected. SQL>
Reference
http://docs.oracle.com/database/121/SBYDB/create_fs.htm#SBYDB5416
