作用：在oracle数据库instance级别的冗余，其中只要有一个instance可用即可保证可用性，但是不能保准数据级别的错误。
数据库文件需要放置在共享存储上，理论上一个实例对应一个数据库，实例间通过内网络进行交互。准确的说rac并非分布式系统。
rac内网用来内部实例间交互数据，保证数据块级别数据的一致性。公网则是和外部联系的接口，rac内网和外网在物理上是分离的。
rac集群下每个数据实例都拥有自己的内存结构、进程及redo文件，redo文件放置在共享磁盘上，各个实例使用自己的redo文件，但是可以访问其他实例的rode文件，如此保证故障恢复的可能性。rac每个实例都拥有自己的undo。
rac容错：其中一个实例荡掉，其他实例读取当机实例的redo文件，进行最后一次checkpoint后redo文件内容的恢复。
rac实例比单实例多出5个进程，主要维护rac各节点访问数据的一致性，也可看成一种锁机制。
独立的服务：crs服务：crs、css进程
数据块的共享：共享锁或排它锁，数据块的传递通过私有网络传送。
vip：虚拟ip，绑定在某个网卡上，当实例当掉后，有会话链接，启到快速报错的目的。解决了网络超时的问题。
ocr：oracle的注册表，保存oracle资源信息。
表决磁盘：决定哪个实例出现了问题。
1、查看RAC服务状态
node1-> crs_stat -t
Name Type Target State Host
------------------------------------------------------------
ora.DATA.dg ora....up.type ONLINE ONLINE node1
ora.FLASH.dg ora....up.type ONLINE ONLINE node1
ora.GRIDDG.dg ora....up.type ONLINE ONLINE node1
ora....ER.lsnr ora....er.type ONLINE ONLINE node1
ora....N1.lsnr ora....er.type ONLINE ONLINE node1
ora.asm ora.asm.type ONLINE ONLINE node1
ora.cvu ora.cvu.type ONLINE ONLINE node1
ora.devdb.db ora....se.type ONLINE OFFLINE
ora.gsd ora.gsd.type OFFLINE OFFLINE
ora....network ora....rk.type ONLINE ONLINE node1
ora....SM1.asm application ONLINE ONLINE node1
ora....E1.lsnr application ONLINE ONLINE node1
ora.node1.gsd application OFFLINE OFFLINE
ora.node1.ons application ONLINE ONLINE node1
ora.node1.vip ora....t1.type ONLINE ONLINE node1
ora....SM2.asm application ONLINE ONLINE node2
ora....E2.lsnr application ONLINE ONLINE node2
ora.node2.gsd application OFFLINE OFFLINE
ora.node2.ons application ONLINE ONLINE node2
ora.node2.vip ora....t1.type ONLINE ONLINE node2
ora.oc4j ora.oc4j.type ONLINE ONLINE node1
ora.ons ora.ons.type ONLINE ONLINE node1
ora....ry.acfs ora....fs.type ONLINE ONLINE node1
ora.scan1.vip ora....ip.type ONLINE ONLINE node1
2、检查CRS的状态
1）查看本地节点CRS状态
node1-> crsctl check crs
CRS-4638: Oracle High Availability Services is online
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
node2-> crsctl check crs
CRS-4638: Oracle High Availability Services is online
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
2）查看集群CRS状态
node1-> crsctl check cluster
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
3）查看evm事件管理器状态
node1-> crsctl check evm
CRS-4533: Event Manager is online
3、查看RAC集群里节点的配置信息
node1-> olsnodes
node1
node2
node1-> olsnodes -n -i -s --- -n列出节点编号 -i列出虚拟ip -s列出状态
node1 1 node1-vip Active
node2 2 node2-vip Active
4、查看RAC集群中软件版本信息
1）查看集群软件使用版本信息
node1-> crsctl query crs activeversion
Oracle Clusterware active version on the cluster is [11.2.0.4.0]
2）查看集群软件发行版本信息
node1-> crsctl query crs releaseversion
Oracle High Availability Services release version on the local node is [11.2.0.4.0]
3）查看集群软件安装版本信息
node1-> crsctl query crs softwareversion
Oracle Clusterware version on node [node1] is [11.2.0.4.0]
5、查看集群软件表决磁盘信息
node1-> crsctl query css votedisk
## STATE File Universal Id File Name Disk group
-- ----- ----------------- --------- ---------
1. ONLINE 2a0486c2db354fbfbf5d5d3b6b2af4fd (ORCL:VOL1) [GRIDDG]
Located 1 voting disk(s).
6、查看系统DNS相关配置信息
node1-> crsctl query dns -servers
CRS-10018: the following configuration was found on the system:
CRS-10019: There are 1 domains in search order. They are:
localdomain
CRS-10022: There are 1 name servers. They are:
172.16.0.191
CRS-10020: number of retry attempts for name lookup is: 4
CRS-10021: timeout for each name lookup is: 5
以上信息来源于：
node1-> cat /etc/resolv.conf
search localdomain
nameserver 172.16.0.191
7、查看集群SCAN VIP信息
node1-> srvctl config scan
SCAN name: scan-cluster.localdomain, Network: 1/172.16.0.0/255.255.240.0/eth0
SCAN VIP name: scan1, IP: /scan-cluster.localdomain/172.16.0.203
node1-> srvctl config scan_listener
SCAN Listener LISTENER_SCAN1 exists. Port: TCP:1521
8、查看OCR信息:集群软件重要部分
[root@node1 bin]# ./ocrcheck -local
Status of Oracle Local Registry is as follows :
Version : 3
Total space (kbytes) : 262120
Used space (kbytes) : 2676
Available space (kbytes) : 259444
ID : 1155296004
Device/File Name : /u01/app/11.2.0/grid/cdata/node1.olr
Device/File integrity check succeeded
Local registry integrity check succeeded
Logical corruption check succeeded
9、查看OCR集群软件备份信息
node1-> ocrconfig -showbackup
node1 2015/04/20 15:58:34 /u01/app/11.2.0/grid/cdata/scan-cluster/backup00.ocr
node1 2015/04/20 15:58:34 /u01/app/11.2.0/grid/cdata/scan-cluster/day.ocr
node1 2015/04/20 15:58:34 /u01/app/11.2.0/grid/cdata/scan-cluster/week.ocr
PROT-25: Manual backups for the Oracle Cluster Registry are not available
10、启、停集群数据库
1）停止RAC数据库
node1-> srvctl stop database -d devdb
2）停止集群服务
[root@node1 ~]# cd /u01/app/11.2.0/grid/bin
[root@node1 bin]# ./crsctl stop cluster -all
3）启动集群服务
[root@node1 bin]# pwd
/u01/app/11.2.0/grid/bin
[root@node1 bin]# ./crsctl start cluster -all
4）启动RAC数据库
node1-> srvctl start database -d devdb
11、验证rac负载均衡
通过windows客户端远程连接test，通过以下语句查询远程连接会话信息：
SQL>select inst_id,username,sid,serial# from gV$session where username='SCOTT';
总结：crs_stat -t crsctl srvctl olsnodes ocrconfig