oracle 单实例 RAC架构 及RAC启动流程
从上面可以看，RAC在后台多了4个进程，RAC原理就是双机可以同时工作，如何保证锁，及块一致性，就用这个4个进程：
LMSn
这个进程是Cache Fusion的主要进程，负责数据块在实例间的传递，对应的服务叫做GCS（Global Cache Service）。这种进程的数量是通过参数GCS_SERVER_PROCESSES来控制，缺省是2个，取值范围是0-9.
LMD
这个进程负责提供的是GES（Global Enqueue Service），具体来说，这个进程负责在多个实例之间协调对数据块的访问顺序，保证数据的一致性。
LMSn、LMD、GRD构成了RAC最核心的功能Cache Fusion。
LCK
负责Non-Cache Fusion资源的同步访问，每个实例有一个LCK进程。
LMON
各个实例的LMON进程会定期通信，以检查集群中各个节点的健康状况，当某个节点出现故障时，负责集群重构、GRD恢复等操作，它提供的服务叫做Cluster Group Services
RAC启动
ohasd负责启动lower stack的集群资源, crsd负责启动上层的集群资源
1 首选找OHAS进程 ，crsctl check has 如果没加，则crsctl check has .
这个可以设置是否随操作系统启动 crsctl enable has crsctl diable has .
2第二步是找CRS，CRS启动会启动ASM VOTING DISK ，这时如果启动有问题，
./crsclt start crs 会报出错误信息，这时根据信息检查
$ORACLE_HOME/log 这是每个集群节点上为oracle集群件以及ASM存储跟踪和诊断日志文件的主目录。
$ORA_CRS_HOME/log/<hostname>/alertHOSTNAME.log 仅包含本地节点上oracle集群件和ASM的跟踪和诊断日志文件。
$ORA_CRS_HOME/log/<hostname>/client 包含各种oracle grid infrastructure客户端(ocrchec,ocrconfig,ocrdump,oifcfg和clscfg等)的跟踪和诊断日志文件。
$ORA_CRS_HOME/log/<hostname>/cssd 包含CSS日志，其中包括来自客户端CSS侦听器的操作，系统会对该日志每20M进行归档一次。
$ORA_CRS_HOME/log/<hostname>/evmd 包含EVM守护进程的跟踪和诊断日志文件。
$ORA_CRS_HOME/log/<hostname>/racg 包含被CRS所管理的资源的日志，也就是所有nodeapp的日志，包括ONS和VIP。
$ORA_CRS_HOME/log/<hostname>/crsd 包含CRSD守护进程的跟踪和调试日志,系统会对该日志每10M进行归档一次。
附为几个进程解释：
・Cluster Synchronization Services (CSS)―Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using third-party clusterware, then the css process interfaces with your clusterware to manage node membership information.
・Cluster Ready Services (CRS)―The primary program for managing high availability operations within a cluster. Anything that the crs process manages is known as a cluster resource which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on. The crs process manages cluster resources based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. The crs process generates events when a resource status changes. When you have installed Oracle RAC, crs monitors the Oracle instance, Listener, and so on, and automatically restarts these components when a failure occurs. By default, the crs process makes five attempts to restart a resource and then does not make further restart attempts if the resource does not restart.
・Event Management (EVM): A background process that publishes events that crs creates.
・Oracle Notification Service (ONS): A publish and subscribe service for communicating Fast Application Notification (FAN) events.
・RACG―Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
・Process Monitor Daemon (OPROCD): This process is locked in memory to monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.