1 2 Previous Next 21 Replies Latest reply on Mar 11, 2016 3:35 AM by Aman....

    ASM striping and mirroring - basic concept

    2982849

      Hi all,

       

      I am thinking that I am having a misconception about ASM mirroring and striping.

      If I have a simple diskgroup with 2 failure groups and  each failure group is having 1 disk. ( 2 way mirror )

       

      So if data1 goes into failuregroup1, it will be mirrored to failure group2 and vice versa.

       

      In that case, how does striping works over here ?  It seems even if we strip across the 2 failure group, the data are still replicated to the other.

       

      How does Oracle knows it can read striped data across the 2 failure groups and not just from 1 group ?

       

      Regards,

      Noob

        • 1. Re: ASM striping and mirroring - basic concept
          Pavan Kumar

          So if data1 goes into failuregroup1, it will be mirrored to failure group2 and vice versa.

           

          In that case, how does striping works over here ?  It seems even if we strip across the 2 failure group, the data are still replicated to the other.

          Its mirroring with in FG group and stripping across different FG group with in your Diskgroup

           

          How does Oracle knows it can read striped data across the 2 failure groups and not just from 1 group ?

          Are you a programmer ? If not then its hard to explain, since algorithms are written to read and track allocation units (of accessing disk headers) files.

           

          - Pavan Kumar N

          1 person found this helpful
          • 2. Re: ASM striping and mirroring - basic concept
            Aman....

            2982849 wrote:

             

            Hi all,

             

            I am thinking that I am having a misconception about ASM mirroring and striping.

            If I have a simple diskgroup with 2 failure groups and  each failure group is having 1 disk. ( 2 way mirror )

             

            So if data1 goes into failuregroup1, it will be mirrored to failure group2 and vice versa.

             

            In that case, how does striping works over here ?  It seems even if we strip across the 2 failure group, the data are still replicated to the other.

             

            How does Oracle knows it can read striped data across the 2 failure groups and not just from 1 group ?

             

            Regards,

            Noob

            Well, the first point is correct. ASM would stripe across ALL the disks -including different failgroups. .It's not important that how many failgroups you create. DO remember that by default, every disk is a part of its own fail group.

             

            For the mirroring, the primary and the mirror copies would be created over different disks. Oracle calls this thing as Partner disks and maintains the information of the primary disks along with their mirror disks(partner) in  a Partner and Status Table(PST). The count of the PST would be depending on the redundancy that you have chosen. So if you have chosen Normal , it would be 2 , for High , it would be 3 and for External , it would be 1( as there would be no mirroring) . It goes more interesting but I shall stop over here with the table name that you can check for the partner disk , x$kfdpartner .

             

            HTH

            Aman....

            1 person found this helpful
            • 3. Re: ASM striping and mirroring - basic concept
              2982849

              Hi Pavan

               

              Thanks for your reply.

              Its mirroring with in FG group and stripping across different FG group with in your Diskgroup

              I thought mirroring are across different FG groups ? - so that mirrored extents do not fall into the same failure group as their primary copy.

               

               

              Regards,

              Noob

              • 4. Re: ASM striping and mirroring - basic concept
                Pavan Kumar

                2982849 wrote:

                 

                Hi Pavan

                 

                Thanks for your reply.

                Its mirroring with in FG group and stripping across different FG group with in your Diskgroup

                I thought mirroring are across different FG groups ? - so that mirrored extents do not fall into the same failure group as their primary copy.

                 

                 

                Regards,

                Noob

                I hope I have commented reverse way(sorry I was working on testing of OGG stuff)

                 

                - Pavan Kumar N

                • 5. Re: ASM striping and mirroring - basic concept
                  Pini Dibask

                  Hello,

                   

                  The following diagram illustrates ASM striping and mirroring capabilities. Each square within the disks represents an Oracle ASM file extent.

                  f1.png

                   

                  As you can see, even inside each Failure Group, Oracle stripes ASM extents, assuming there is more than 1 disk in each failure group.

                  This diagram is taken from my article which describes Oracle Automatic Storage Management's mirroring and striping capabilities: Verifying I/O Activity Balance Across Disks in ASM

                   

                  If you have any further questions, let us know.

                  1 person found this helpful
                  • 6. Re: ASM striping and mirroring - basic concept
                    OrcL-FaN

                    @2982849 ,

                     

                    Hello, though there are lot of materials in google, but i find this one interesting. Just type julian dyke oracle asm ppt in google and download the ppt. Hope you will find it informative because that ppt has been made excellently.

                     

                    Thanks,

                    Pinto

                    1 person found this helpful
                    • 7. Re: ASM striping and mirroring - basic concept
                      2982849

                      Hi Aman..

                       

                      Thanks for your input.

                      You mentioned that ASM will stripped across all the disks in the disk group.

                       

                      So mirroring can be defined externally (no mirror) but striping is always "ON" ?

                       

                      Regards,

                      Noob

                      • 8. Re: ASM striping and mirroring - basic concept
                        Pini Dibask

                        Hi,

                         

                        So mirroring can be defined externally (no mirror) but striping is always "ON" ?

                         

                        Yes, as long as you have more than 1 ASM disk in your Disk Group.

                        1 person found this helpful
                        • 9. Re: ASM striping and mirroring - basic concept
                          2982849

                          Hi Pini,

                           

                          Thanks for the nice illustration.

                          I would like to double confirm with you on 1 point mentioned by you

                          As you can see, even inside each Failure Group, Oracle stripes ASM extents, assuming there is more than 1 disk in each failure group.

                           

                          Do you mean striping will not occur if there are only 1 disk inside the failure group ?  I thought that ASM will strip across all the disks in the diskgroup (including the different failure groups)

                           

                          e.g. extent1 - assigned to Failure group A  (which its partner get mirrored to Failure group B)

                                 extent2 - assigned to Failure group B (which its partner get mirror to Failure group A)

                                 extent3 - assigned to Failure group A  (which its partner get mirrored to Failure group B) ..

                                 ... and goes on.

                           

                           

                          Regards,

                          Noob

                          • 10. Re: ASM striping and mirroring - basic concept
                            Pini Dibask

                            Hi,

                             

                            Oracle ASM mirrors ASM extents across the different fail groups (as you can see in the above illustration).

                            For example, in the normal redundancy ASM disk Group, each file extent has a copy in a seperate fail group (also called two-way mirroring), so it is not striping, but rather mirroring.

                            The striping will occur across the disks within the same fail group.

                             

                            • 11. Re: ASM striping and mirroring - basic concept
                              rchem

                              @pini dibask

                              The striping will occur across the disks within the same fail group.

                               

                              If there is only one disk for failure group, then striping doesn't happen across failure groups?  I have verified the extents will spread across failure groups.

                              1 person found this helpful
                              • 12. Re: ASM striping and mirroring - basic concept
                                Dude!

                                I suggest not to confuse ASM with RAID. ASM mirrors files, not disks. ASM writes to all disks in a round robin fashion and attempts fill all disks evenly. Mirroring of data is only between failure groups. If you specify external ASM redundancy, there is no mirroring of data.

                                1 person found this helpful
                                • 13. Re: ASM striping and mirroring - basic concept
                                  Pini Dibask

                                  Exactly.

                                  Oracle ASM will stripe the data in small chunks of 128 KB for lower I/O latency for small I/O operations such as writing redo log entries to the redo log files (fine-grained striping). For data files, for example, Oracle ASM will stripe the data in bigger chunks that are equal to the Allocation Unit Size (coarse-grained striping).

                                  • 14. Re: ASM striping and mirroring - basic concept
                                    2982849

                                    Hi rchem,

                                     

                                    Can i know which view/internal view you use to verify where the primary extent and its partner is at ?

                                     

                                    Regards,

                                    Noob

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