环境：Mysql+heartbeat+drbd 架构

    问题：mysql-主 宕机 mysql-从接替之后，再恢复Mysql-主之后，发现主的drbd启动不了，而且从上面也无法辨识对方，从的状态是Primary/Unknown ，主的状态是Secondary/Unknown 

         查看从节点的日志发现脑裂：
[root@node2 ~]# tail -n 12 /var/log/messages 
Sep 21 11:19:53 lab4 kernel: block drbd0: Split-Brain detected but unresolved, dropping connection! 
Sep 21 11:19:53 lab4 kernel: block drbd0: helper command: /sbin/drbdadm split-brain minor-0 
Sep 21 11:19:53 lab4 kernel: block drbd0: helper command: /sbin/drbdadm split-brain minor-0 exit code 0 (0x0) 
Sep 21 11:19:53 lab4 kernel: block drbd0: conn( WFReportParams -> Disconnecting ) 
Sep 21 11:19:53 lab4 kernel: block drbd0: error receiving ReportState, l: 4! 
Sep 21 11:19:53 lab4 kernel: block drbd0: meta connection shut down by peer. 
Sep 21 11:19:53 lab4 kernel: block drbd0: asender terminated 
Sep 21 11:19:53 lab4 kernel: block drbd0: Terminating drbd0_asender 
Sep 21 11:19:53 lab4 kernel: block drbd0: Connection closed 
Sep 21 11:19:53 lab4 kernel: block drbd0: conn( Disconnecting -> StandAlone ) 
Sep 21 11:19:53 lab4 kernel: block drbd0: receiver terminated 
Sep 21 11:19:53 lab4 kernel: block drbd0: Terminating drbd0_receiver

           此时的环境是从节点的heartbeat、mysql启动，顶替主的工作，从节点的drbd状态是Primary/Unknown，并且已经挂载着  /dev/drbd0  /data  ，主节点的状态是未启动heartbeat和mysql 并且启动drbd的时候报错。

             

恢复过程：

               

将主节点设置为从节点并丢弃资源数据
[root@node1 ~]# drbdadm secondary r0
[root@node1 ~]# drbdadm -- --discard-my-data connect r0

在从节点上手动连接资源
[root@node2 ~]# drbdadm connect r0


最后查看节点状态，连接已恢复正常
[root@node1 ~]# cat /proc/drbd        
version: 8.3.15 (api:88/proto:86-97) 
GIT-hash: 0ce4d235fc02b5c53c1c52c53433d11a694eab8c build by [email protected], 2013-03-27 16:04:08 
 0: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r----- 
    ns:36 nr:0 dw:24 dr:185 al:0 bm:1 lo:0 pe:0 ua:0 ap:0 ep:1 wo:b oos:0


此时再启动主节点的heartbeat 即可！