How Oracle Cluster Starts
When considering how Oracle Clusterware is able to store vital files (OCR and Voting Files) in an ASM Diskgroup, and while ASM is itself dependent on Oracle Clusterware.
The following is a brief overview of the logic used for starting Oracle Clusterware with ASM when clusterware files; OCR and Voting Files, are stored in an ASM Diskgroup. Note, that there are configuration dependent variations to the following logic, but what is described is the most common case.
1.When a node of an Oracle Clusterware cluster restarts, OHASD is started by platform-specific means. OHASD is the root for bringing up Oracle Clusterware. OHASD has access to the OLR (Oracle Local Registry) stored on the local file system. OLR provides needed data to complete OHASD initialization
2.OHASD brings up GPNPD and CSSD. CSSD has access to the GPNP Profile stored on the local file system. This profile contains the following vital bootstrap data;
a.ASM Diskgroup Discovery String
b.ASM SPFILE location (Diskgroup name)
c.Name of the ASM Diskgroup containing the Voting Files
3.The Voting Files locations on ASM Disks are accessed by CSSD with well-known pointers in the ASM Disk headers and CSSD is able to complete initialization and start or join an existing cluster.
4.OHASD starts an ASM instance and ASM can now operate with CSSD initialized and operating. The ASM instance uses special code to locate the contents of the ASM SPFILE, assuming it is stored in a Diskgroup.
5.With an ASM instance operating and its Diskgroups mounted, access to Clusterware’s OCR is available to CRSD.
6.OHASD starts CRSD with access to the OCR in an ASM Diskgroup.
7.Clusterware completes initialization and brings up other services under its control.
OLR holds metadata for the local node and in conjunction with GPnP profile OHASD has all the information required initially to join the node to the cluster and OHASD manages OLR. so both OLR and GPnP profile is essential and required.
In RAC, exactly from gpnp profile cssd gets all required information to get hold of maximum number of voting disk to start cssd .
While doing to as asm_diskstring parameter ,it searches all the disk for voting file signature .
When it completes the search ,writes how many voting file it found and start cssd . those information you can see on any RAC node using below command from OS user which is holding GI .
$ gpnptool get
You can see asm_disktring value on above output .
If your system is using default path as per OS, then it will be blank.
In Case of Non-RAC, there is no such use of gpnp.
Only OLR is being used to initialize ohasd.
ASMCMD>DSGET
To fetch the ASM diskstring. The ASMCMD will work in both RAC and NON-RAC environment.
When considering how Oracle Clusterware is able to store vital files (OCR and Voting Files) in an ASM Diskgroup, and while ASM is itself dependent on Oracle Clusterware.
The following is a brief overview of the logic used for starting Oracle Clusterware with ASM when clusterware files; OCR and Voting Files, are stored in an ASM Diskgroup. Note, that there are configuration dependent variations to the following logic, but what is described is the most common case.
1.When a node of an Oracle Clusterware cluster restarts, OHASD is started by platform-specific means. OHASD is the root for bringing up Oracle Clusterware. OHASD has access to the OLR (Oracle Local Registry) stored on the local file system. OLR provides needed data to complete OHASD initialization
2.OHASD brings up GPNPD and CSSD. CSSD has access to the GPNP Profile stored on the local file system. This profile contains the following vital bootstrap data;
a.ASM Diskgroup Discovery String
b.ASM SPFILE location (Diskgroup name)
c.Name of the ASM Diskgroup containing the Voting Files
3.The Voting Files locations on ASM Disks are accessed by CSSD with well-known pointers in the ASM Disk headers and CSSD is able to complete initialization and start or join an existing cluster.
4.OHASD starts an ASM instance and ASM can now operate with CSSD initialized and operating. The ASM instance uses special code to locate the contents of the ASM SPFILE, assuming it is stored in a Diskgroup.
5.With an ASM instance operating and its Diskgroups mounted, access to Clusterware’s OCR is available to CRSD.
6.OHASD starts CRSD with access to the OCR in an ASM Diskgroup.
7.Clusterware completes initialization and brings up other services under its control.
OLR holds metadata for the local node and in conjunction with GPnP profile OHASD has all the information required initially to join the node to the cluster and OHASD manages OLR. so both OLR and GPnP profile is essential and required.
In RAC, exactly from gpnp profile cssd gets all required information to get hold of maximum number of voting disk to start cssd .
While doing to as asm_diskstring parameter ,it searches all the disk for voting file signature .
When it completes the search ,writes how many voting file it found and start cssd . those information you can see on any RAC node using below command from OS user which is holding GI .
$ gpnptool get
You can see asm_disktring value on above output .
If your system is using default path as per OS, then it will be blank.
In Case of Non-RAC, there is no such use of gpnp.
Only OLR is being used to initialize ohasd.
ASMCMD>DSGET
To fetch the ASM diskstring. The ASMCMD will work in both RAC and NON-RAC environment.
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