Clusterware Startup Sequence--11gR2 Clusterware and Grid Home - What You Need to Know [ID 1053147.1]

Clusterware Startup Sequence

The following is the Clusterware startup sequence (image from the "Oracle Clusterware Administration and Deployment Guide):

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: