Some of the key facts of 11gR2 Clusterware

  1. The GRID home consists of the Oracle Clusterware and ASM.
  2. The 11gR2 Clusterware can be installed in “Standalone” mode for ASM.

  • OCR and Voting files can either be on CFS or ASM.
  • OCR is backed up automatically every 4 hours to
  • GRID_HOME:/cdata/<scan name;/ and can be restored via ocrconfig.
  • Voting file is backed up into the OCR at every configuration change and can be restored via crsctl.
  • 11gR2 Clusterware requires at least one private network for inter-node communication and at least one public network for external communication.Several VIP’s registered with DNS.
  • A SCAN (Single Client Access Name) is provided to clients.
  • The script at the end of the clusterware installation starts the clusterware stack.
  • On Unix, the clusterware stack is started via the init.ohasd script referenced in /etc/inittab with “respawn”.
  • A node can be evicted (rebooted) if a node is deemed to be unhealthy.  This is done so that the health of the entire cluster can be maintained.

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 &amp; 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


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