Oracle Clusterware Concepts

Oracle Clusterware Concepts:

Oracle Clusterware is the heart of Oracle RAC Database. Clusterware concepts are very important for a DBA to ride Oracle RAC Databases. The main concepts of Oracle Clusterware are as follows.

Oracle Clusterware mainly has 2 components,

  1. Voting Disk
  2. Oracle Cluster Registry


Voting Disk:

Voting disk is to determine which nodes are members of a cluster. You can configure them on an ASM or a shared storage

Oracle Cluster Registry:

Oracle Clusterware uses OCR to store, manage information about components that Clusterware controls (eg: RAC Databases, Listsners, SCAN listeners, VIPs, Services etc). OCR stores information in a series of key-value pairs in tree structure.

You can update OCR using supported utilities like OEM (Oracle Enterprise Manager), CRSCTL (Clusterware Control Utility), SRVCTL (Server Control Utility), OCRCONFIG (OCR Configuration Utility), DBCA (DB Configuration Assistant)

Now, lets see what are the Software Clusterware Components,

Clusterware Software components has two stacks,

  1. The Cluster Ready Services Stack (Called Upper Stack) – Anchored by CRS Daemon (crsd)
  2. Oracle High Availability Services Stack (Called Lower Stack) – Anchored by Oracle High Availability Services Daemon (ohasd)

CRSD Stack:

CRSD Stack manages multiple services in a cluster. Below are few,

  • CRS – CRS Daemon based on configuration information that is stored in OCR, includes start/stop/monitor/failover
  • CSS – Cluster Synchronization Services – Manages by controlling which nodes are members of cluster & notifies members when a node joins or leaves (cssdagent)
  • Oracle ASM – Disk Management
  • CTSS – Cluster Time Synchronization Services
  • EVM – Event Management
  • ONS – Oracle Notification Services
  • Oraagent – Oracle Agent, this process runs Server Callouts when FAN Agent occurs
  • Orarootagent – helps crsd manage resources owned by root, such as Network, Grid Virtual IP addr

Oracle High Availability Stack:

Ohasd manages the below services,

  • Ologgerd – Cluster Logger Service. Receives info from all nodes in a cluster. This can run on only 2 nodes
  • Osysmond – Monitors OS metric collection, sends info to Cluster Logger Service
  • GPNPD – Grid Plug & Play. Provides access to Grid Plug & Play profile among the nodes of cluster to ensure all nodes are with latest profile
  • GIPC – Grid Interprocess Communication. Daemon that enables Redundant Interconnect usages
  • MDNS – Multicast Domain Name Service
  • GNS – Grid Naming Service


Managing Clusterware Services:

You can manage Cluster ware using the below utilities,

  • OEM
  • CVU (Cluster Verification Utility)
  • Srvctl (Server Control)
  • Crsctl (Clusterware Control)
  • Oifcfg (Oracle Interface Configuration Tool) – For network related setup à Oracheck, oradump
  • CHM (Cluster Health Monitor)


Managing OCR & Voting Disks:

Few important Commands:

  • Crsctl query crs activeversion
  • Oracheck
  • Crsctl check crs
  • Oraconfig –showbackup
  • Ocrdump –backup <backup file name and location>
  • Olsnodes
  • Crsctl start crs –excl – nocrs (Starting in Exclusive mode without starting other components of CRS)
  • Ocrconfig –restore <backup file with location>
  • Cluvfy comp ocr –n all –verbose
  • Crsctl start has
  • Crsctl stop crs
  • Crsctl stop crs –f


Oracle Cluster Registry:

  • Oracheck –local
  • Ocrconfig –local – manual backup
  • Crsctl query css votingdisk
  • Crsctl delete css votingdisk <Path and name>
  • Crsctl add crs votedisk <path>
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