6 Replies Latest reply: Jul 10, 2013 5:08 AM by Ed Rudans RSS

    Questions on asm disk discovery:

    user586723

      Questions on asm disk discovery:

       

      1)What is the relationship btween asm_diskstring in the init.ora and DiscoveryString in the GPNP profile.xml?

       

      2)  Which one of the above two finally accounts for the disk discovery process?

       

      3)  We know that asmlib disks are self describing at the disk header. This overcomes the disk name/path persistency issue as we no long need to rely on the path to discover the asm disks, by setting asm_diskstring='ORCL:*' , ASM instance will identify the right disks automatically. However, I am not sure if setting asm_diskstring='ORCL:*' is the most economic way to do the discovery as I am not sure if Oracle will have to probe all the disks on the OS to determine the right disks. If Oracle has to screen all the disks in this way, then I think setting asm_diskstring='<path_to_asmlib_disk>' will be much faster, although this will be open to the persistent problem. Is my understanding correct?

       

      Thanks.

        • 1. Re: Questions on asm disk discovery:
          rarain

          Hi,

           

          DiscoveryString in GPNP profile.xml is basically used by clusterware to scan all disks header which match the pattern in order to identify Voting Disks and Disk containing ASM SPFILE because it is required before to start ASM instance.

          ASM_DISKSTRING in ASM Parameter file is used to scan all disks header which match the pattern for mounting the diskgroup.

           

          Thanks

          • 2. Re: Questions on asm disk discovery:
            user586723

            Thanks your comments on GPNP profile.

            By setting asm_diskstring='' o 'ORCL:*', will oracle scan and probe all the disks on the OS or just scan the /dev/oracleasm/disks direcotry for the asmlib created disks? Does anyone have a definite answer?

             

            Thanks,

            Alex

            • 3. Re: Questions on asm disk discovery:
              user586723

              There was a typo error in the previous post. It should be:

               

              By setting asm_diskstring='', that is, null or 'ORCL:*', will oracle scan and probe all the disks on the OS or just scan the /dev/oracleasm/disks directory for the asmlib created disks? Does anyone have a definite answer?

               

              Many thanks,

              Alex

              • 5. Re: Questions on asm disk discovery:
                1022508

                Good question. I also wonder for the asmlib created disks, by setting asm_diskstring='ORCL:*', will the asm instance probe all the disks in general or just scan the disks under /dev/oracleasm/disks and verify if their heads contains the 'ORCL' like strings.

                 

                Is this a very trivial question or no one is sure about that exactly the process involved?

                • 6. Re: Questions on asm disk discovery:
                  Ed Rudans

                  From my understanding all disk you see in /dev/oracleasm/disks are the disks in your system that been discovered by asmlib at discovery stage.

                  Currently, due to bug 13465545, ASM instance will discover disks from both locations, ASM_DISKSTRING and gpnp profile, which can cause some mess in disk representation for asm. You can check the settings using asmcmd command: dsget, and set to be the same using dsset.

                  I think its more secure to set ASM_DISKSTRING to only the disks used by asm instance.

                  ASMCMD> dsget

                   

                  Regards

                  Ed