雙機互備和熱備的區別：
互備所指的是backup,保證數據的完整性而做的備份。主要目的是防止數據丟失。
熱備是爲了保證應用的連續性。利用故障轉移的方法實現。
Linux下實現的雙機互備：
主從備份：
1、設置同步Master
修改 my.cnf 文件，在
# Replication Master Server (default)
# binary logging is required for replication
添加如下內容：
#log-bin=/var/log/mysql/updatelog
server-id = 1
binlog-do-db=discuz
binlog-ignore-db=mysql
重啓MySQL,創建一個MySQL帳號爲同步專用
# /usr/local/mysql/bin/mysql -u root -p
mysql> GRANT REPLICATION SLAVE ON *.* TO [email=]'back'@'%'[/email] IDENTIFIED BY 'back';
如果想要在Slave上有權限執行 "LOAD TABLE FROM MASTER" 或 "LOAD DATA FROM MASTER" 語句的話，必須授予全局的 FILE 和 SELECT 權限：
mysql>GRANT FILE,SELECT,REPLICATION SLAVE ON *.* TO [email=]'back'@'%'[/email] IDENTIFIED BY 'back';
mysql> FLUSH PRIVILEGES ;
2、設置同步Slave
修改my.cnf文件，添加
server-id = 2
master-host = 192.168.1.123
master-user = back
master-password = back
master-port = 3306
replicate-ignore-db=mysql
replicate-do-db=discuz
重啓MySQL
3、啓動同步
在主服務器master MySQL命令符下
view plaincopy to clipboardprint?# /usr/local/mysql/bin/mysql -u root -p
mysql> show master status;
顯示（當然這個是我機器的情況，你的不可能跟我一樣哈，只是個例子）：
+------------------+----------+-------------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+-------------------+------------------+
| mysql-bin.000009 | 98 | discuz | mysql |
+------------------+----------+-------------------+------------------+
在從服務器master MySQL命令符下
view plaincopy to clipboardprint?# /usr/local/mysql/bin/mysql -u root -p
mysql> slave stop;
mysql> change master to master_host='192.168.1.123', master_user='back', master_password='back', master_log_file='mysql-bin.000009', master_log_pos=98;
mysql> slave start;
用show slave status/G;看一下從服務器的同步情況
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
如果都是yes，那代表已經在同步
往表裏面寫點數據測試一下看是否同步成功，如果不成功，絕對不是你的RP問題，再檢查一下操作步驟！
4、設置雙向同步
修改slave服務器的my.cnf，添加
log-bin=/var/log/mysql/updatelog
binlog-do-db=discuz
binlog-ignore-db=mysql
重啓MySQL,創建一個MySQL帳號爲同步專用
view plaincopy to clipboardprint?mysql> GRANT REPLICATION SLAVE ON *.* TO [email=]'back'@'%'[/email] IDENTIFIED BY 'back';
mysql> GRANT FILE,SELECT,REPLICATION SLAVE ON *.* TO [email=]'back'@'%'[/email] IDENTIFIED BY 'back';
mysql> FLUSH PRIVILEGES ;
修改master服務器的my.cnf,添加
master-host = 192.168.1.124
master-user = back
master-password = back
master-port = 3306
replicate-ignore-db=mysql
replicate-do-db=discuz
重啓MySQL
在主服務器slave MySQL命令符下：
show master status;
+------------------+----------+-------------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+-------------------+------------------+
| mysql-bin.000013 | 98 | discuz | mysql |
+------------------+----------+-------------------+------------------+
在服務器A MySQL命令符下：
view plaincopy to clipboardprint?mysql> slave stop；
mysql> change master to master_host='192.168.1.124', master_user='back', master_password='back', master_log_file='mysql-bin.000013', master_log_pos=98;
mysql> slave start;
mysql> slave stop；
mysql> change master to master_host='192.168.1.124', master_user='back', master_password='back', master_log_file='mysql-bin.000013', master_log_pos=98;
mysql> slave start;
mysql做互備時要注意mysql 5.5以上版本不能把
master-host = 192.168.1.124
master-user = back
master-password = back
master-port = 3306
寫道my.ini文件中。要在執行完 slave stop;後 用 change master to master_host='主的ip',master_user='用戶名',mater_password='密碼',master_log_file='日誌',master_log_pos='同步點';
然後slave status;