How to modify Voting disks in ASM

The process for modifying a votedisk that is stored on ASM differs from the process when the votedisk is stored on some other medium.

When your voting disks are stored on ASM you can move them off to non ASM storage with the replace command:

$ crsctl replace votedisk [path_to_new_votedisk]

(this can be done from any node.

The opposite is much the same and you can move all of the disks when they are not on ASM , to ASM with the replace command:

$ crsctl replace votedisk +[asm_diskgroup]

When you are not using ASM storage for your voting disks, the procedure is much the same but there are differences because, where ASM handles the replication of voting disks (you specify one disk and it is replicated depending on the protection level of your ASM disk group), when you are not using ASM, you need to manually create disks to handle replication.

You add a voting disk with the command:

$ crsctl add css votedisk [path to vote disk]

you can also delete a votedisk with the following command:

$ crsctl delete css votedisk [path the votedisk]

The only slightly more complicated option is if you want to replace the votedisk. in this case, you need to create a new one and delete the old one in one command. this is done with the ‘purge’ option which deletes the disk.

$ crsctl add css votedisk [path to votedisk] -purge

 

How ASM Dynamic Volume Manager presents its Volumes.

An ASM instance forms and presents is the underlying structure for an ASM dynamic volume.

ASM provides a disk group which is really a logical container for physical space. ASM is very efficient at storing data files but there are many types of files that cannot be stored on ASM and it cannot be read directly by the OS.

In order to expand the functionality of ASM, ADVM was introduced to allow more file types to be stored on ASM managed storage.

ADVM allows you to create a volume on an ASM disk that can be presented to the operating system where a file system (such as ACFS) can be created and that can store most of your database related files as well as other ‘normal’ files that you might wish to place there. The big advantage being that it is backed up by ASM.

Some kernel modules are necessary to provide this service. They are:

  • ¬†oracleasm – the asm module.
  • oracleadvm – the ASM dynamic Volume manager module.
  • oracleoks – the kernel services module.
  • oracleacfs – the ASM file system module.

You can not use ACFS (Oracle Cluster File Systems) to store:

  • ¬†Oracle Base Directory.
  • Oracle Grid infrastructure home that contains software for Oracle clusterware, ASM, Oracle ACFS or Oracle ADVM components.
  • OS root directory
  • Boot directory

 

 

 

How is the SGA in an ASM instance made up

An ASM instance has its own SGA but it is not the same as the SGA in a database instance.

The 4 main sections of the SGA in an ASM instance are:

  • ASM Cache – this is used during rebalancing operations for reding and writing blocks.
  • Large Pool – Used for Parallel Operations.
  • Shared Pool – Stored Metadata information.
  • Free Memory – Memory that is not currently allocated.

How to create more copies of Voting Disks in Oracle 11g RAC

You cannot simply add more copies of voting disks to increase redundancy because the number of voting disks is managed by Oracle ASM and determined by the redundancy of the disk group.

To increase the number of voting disks, you need to move them to a disk group with higher redundancy.

So, create the new disk group or identify one that meets your requirements and use the:

crsctl replace votedisk command to move your voting disks to the new disk group.

Automatic OCR backups

Oracle CRS backs up the OCR automatically at regular intervals.

The standard backup frequency and retention policies are

  • Every 4 hours – keeping the last 3 copies.
  • Every day (at the end) – keeping the last 2 copies.
  • Every week (at the end) – keeping the last 2 copies.

 

You can find the location of the backup as well as which node carries out the backup (only one node backs up the OCR) with the following command:

ocrconfig -showbackup auto

The files may not all be on the node that caries out the backups because of outages.