For whoever that has worked with the 11gR2 version of RAC , has ran into the startup sequence diagram, this diagram is just disturbing to see, I don’t know about you, but for me is just unhelpful and not KISS.

Then there is the second diagram available, which is way more clear, but in a very bad quality, you actually have to squint your eyes, and for me, and my very bad eyesight this is not good, even not understanding what it said.

Now, I’m not inventing the wheel with this diagram, I’m just making it more readable for whoever wants to look at it.The full description, the really unreadable diagram and/or any updates to this you can find it in MOS Document 1053147.1

Click on the image below to see the full size

This description is also from the MOS note stated above

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:
    CSDD (ora.cssd)     – Cluster Synchronization Services
    CRSD(ora.crsd)     – Primary daemon responsible for managing cluster resources.
    CTSSD(ora.ctssd)     – Cluster Time Synchronization Services Daemon
    Diskmon(ora.diskmon)
    ACFS (ASM Cluster File System) Drivers

Level 2: OHASD oraagent spawns:

    MDNSD(ora.mdnsd)     – Used for DNS lookup
    GIPCD(ora.gipcd)     – Used for inter-process and inter-node communication
    GPNPD(ora.gpnpd)     – Grid Plug & Play Profile Daemon
    EVMD(ora.evmd)     – Event Monitor Daemon
    ASM(ora.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