Oracle RAC Clusterware startup sequence 11gR2

Clusterware startup sequence 11gR2

Don't let this picture scare you too much.  You aren't responsible for managing all of these processes, that is the Clusterware's job!

Short summary of the startup sequence: INIT spawns init.ohasd (with respawn) which in turn starts the OHASD process (Oracle High Availability Services Daemon).  This daemon spawns 4 processes.

Level 1: OHASD Spawns:

• cssdagent - Agent responsible for spawning CSSD.
• orarootagent - Agent responsible for managing all root owned ohasd resources.
• oraagent - Agent responsible for managing all oracle owned ohasd resources.
• cssdmonitor - Monitors CSSD and node health (along wth the cssdagent).

Level 2: OHASD rootagent spawns:

• CRSD - Primary daemon responsible for managing cluster resources.
• CTSSD - Cluster Time Synchronization Services Daemon
• Diskmon
• ACFS (ASM Cluster File System) Drivers 

Level 2: OHASD oraagent spawns:

• MDNSD - Used for DNS lookup
• GIPCD - Used for inter-process and inter-node communication
• GPNPD - Grid Plug & Play Profile Daemon
• EVMD - Event Monitor Daemon
• ASM - Resource for monitoring ASM instances

Level 3: CRSD spawns:

• orarootagent - Agent responsible for managing all root owned crsd resources.
• oraagent - Agent responsible for managing all oracle owned crsd resources.

Level 4: CRSD rootagent spawns:

• Network resource - To monitor the public network
• SCAN VIP(s) - Single Client Access Name Virtual IPs
• Node VIPs - One per node
• ACFS Registery - For mounting ASM Cluster File System
• GNS VIP (optional) - VIP for GNS

Level 4: CRSD oraagent spawns:

• ASM Resouce - ASM Instance(s) resource
• Diskgroup - Used for managing/monitoring ASM diskgroups.  
• DB Resource - Used for monitoring and managing the DB and instances
• SCAN Listener - Listener for single client access name, listening on SCAN VIP
• Listener - Node listener listening on the Node VIP
• Services - Used for monitoring and managing services
• ONS - Oracle Notification Service
• eONS - Enhanced Oracle Notification Service
• GSD - For 9i backward compatibility
• GNS (optional) - Grid Naming Service - Performs name resolution

This image shows the various levels more clearly:

OHASD Phase:-

• OHASD (Oracle High Availability Server Daemon) starts Firsts and it will start

OHASD Agent Phase:-

• OHASD Agent starts and in turn this will start

gipcd	Grid interprocess communication daemon, used for monitoring cluster interconnect
mdnsd	Multicast DNS service It resolves DNS requests on behalf of GNS
gns	The Grid Naming Service (GNS), a gateway between DNS and mdnsd, resolves DNS requests
gpnpd	Grid Plug and Play Daemon, Basically a profile similar like OCR contents stored in XML format in $GI_HOME/gpnp/profiles/ etc., this is where used by OCSSD also to read the ASM disk locations to start up with out having ASM to be up, moreover this also provides the plug and play profile where this can be distributed across nodes to cluster
evmd/ evmlogger	Evm service will be provided by evmd daemon, which is a information about events happening in cluster, stop node,start node, start instance etc.

• cssdagent (cluster synchronization service agent), in turn starts

ocssd

Cluster synchronization service daemon which manages node membership in the cluster

If cssd found that ocssd is down, it will reboot the node to protect the data integrity.

• cssdmonitor (cluster synchronization service monitor), replaces oprocd and provides I/O fencing

• OHASD orarootagent starts and in turn starts

crsd.bin	Cluster ready services, which manages high availability of cluster resources , like stopping , starting, failing over etc.
diskmon.bin	disk monitor (diskdaemon monitor) provides I/O fencing for exadata storage
octssd.bin	Cluster synchronization time services , provides Network time protocol services but manages its own rather depending on OS

CRSD Agent Phase:- crsd.bin starts two more agents

crsd orarootagent(Oracle root agent) starts and in turn this will start

gns	Grid interprocess communication daemon, used for monitoring cluster interconnect
gns vip	Multicast DNS service It resolves DNS requests on behalf of GNS
Network	Monitor the additional networks to provide HAIP to cluster interconnects
Scan vip	Monitor the scan vip, if found fail or unreachable failed to other node
Node vip	Monitor the node vip, if found fail or unreachable failed to other node

crsd oraagent(Oracle Agent) starts and in turn it will start (the same functionality in 11gr1 and 10g managed by racgmain and racgimon background process) which is now managed by crs Oracle agent itself.

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ASM & disk groups	Start & monitor local asm instance
ONS	FAN feature, provides notification to interested client
eONS	FAN feature, provides notification to interested client
SCAN Listener	Start & Monitor scan listener
Node Listener	Start & monitor the node listener (rdbms?)