Friday, 11 October 2013

Oracle RAC: 11gR2 Clusterware Startup Order

ASM does not depend on CRS to start. ASM depends on Voting Disk which is accessed directly on Lun (without ASM).

Startup Sequence

init -> OHAS (OLR) -> CSSD/ASM (access ASMDISK/LUN and read Voting Disks) -> CRSD (open DISKGROUP and read OCR)

There are many improvements in version 11.2.

When Clusterware starts three files are involved.

OLR - Is the first file to be read and opened. This file is local and this file contains information regarding where the voting disk is stored 

and information to startup the ASM. (e.g ASM DiscoveryString) 

VOTING DISK - This is the second file to be opened and read, this is dependent on only OLR being accessible.

ASM starts after CSSD or ASM does not start if CSSD is offline (i.e voting file missing)

How are Voting Disks stored in ASM?

Voting disks are placed directly on ASMDISK. Oracle Clusterware will store the votedisk on the disk within a disk group that holds the Voting Files. 
Oracle Clusterware does not rely on ASM to access the Voting Files, which means Oracle Clusterware does not need of Diskgroup to read and write on ASMDISK. It is possible to check for existence of voting files on a ASMDISK using the V$ASM_DISK column VOTING_FILE.
So, voting files not depend of Diskgroup to be accessed, does not mean that the diskgroup is not needed, diskgroup and voting file are linked by their settings.

OCR - Finally the ASM Instance starts and mount all Diskgroups, then Clusterware Deamon (CRSD) opens and reads the OCR which is stored on Diskgroup.

So, if ASM already started, ASM does not depend on OCR or OLR to be online. ASM depends on CSSD (Votedisk) to be online.

There is an exclusive mode to start ASM without CSSD (but it's to restore OCR or VOTE purposes)

No comments:

Post a Comment

Number of Visitors