11 Replies Latest reply on Jun 9, 2016 1:11 PM by Dude!

    Is it advisable to have ASM normal redundancy if storage already have RAID 10

    ivwvi

      Dear Experts,

       

      Is it advisable to have ASM normal redundancy if storage already have RAID 10 .

       

      At storage level disk-groups have RAID 10 for +DATA and  +FRA.

       

       

      I am trying to understand the below oracle recommended

      Use the storage array hardware RAID 1 mirroring protection when possible to reduce the mirroring overhead on the server.

      Use ASM mirroring redundancy in the absence of a hardware RAID,

      or when you need host-based volume management functionality, such as mirroring across storage systems.

      What is need of host-based volume management functionality?



      Thanks & Regards,

      ivw

        • 1. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
          Pavan Kumar

          Is it advisable to have ASM normal redundancy if storage already have RAID 10 .

          When you data is protected at hardware level using RAID, why you want to impose further the redundancy on top of it @software level using ASM. Better you can opt for external redundancy.

          Answer exists in your quoted statement " Use ASM mirroring redundancy in the absence of a hardware RAID"

           

          - Pavan Kumar N

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          • 2. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
            SUPRIYO DEY

            It is not recommended as the mirroring is already done at the RAID level. So Double mirroring will impact the performance of DB.

            1 person found this helpful
            • 3. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
              Bunditj

              Hello,

               

              Is it advisable to have ASM normal redundancy if storage already have RAID 10 ?

              Ans: If your storage subsystem has well-rounded protection on hardware level, you don't have to doubly protect your data on ASM level at all. It will put some overhead of protection and confusion to administration.


              What is need of host-based volume management functionality?

              Ans: If you can't take any advantage on hardware level (RAID protection on storage subsystem), there is another protection e.g.

              - host level (or host-based volume management). Most platform can provide you a mirroring volume e.g you have 2 logical units (LUN) assigned to your database server, but 1st LUN is your primary volume, the 2nd one is your mirrored volume as protection.

                - ASM level, that you could possibly choose either normal redundancy (2-way mirroring + stripped), or high redundancy (3-way mirroring + stripped). For non-exadata, you are eligible to choose external redundancy which of course you decide to use storage subsystem as protection.


              Cheers,

              Bunditj

              1 person found this helpful
              • 4. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                Aman....

                Good to see over the forums my friend .

                 

                Aman....

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                • 5. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                  Aman....

                  Is it advisable to have ASM normal redundancy if storage already have RAID 10 .

                   

                  Advisable, no. Should ? May be! The thing is RAID 10 is Stripe and Mirror. Now, with ASM striping is inevitable. And with ASM striping the chunks are created on the file level. So this means, if you are going to be doing striping from the storage level also, the stripe chunk must be as close as possible to the stripe chunk that's used by ASM(128KB, 1MB) . If not that's going to be now an overhead to maintain dissimilar stripe chunks. So using storage level striping over ASM is not really much of any use.

                   

                  About RAID 1, which is mirroring, the only benefit that you are going to get is that since redundancy is maintained on teh storage level, ASM won't need to reserve any space in order to create the chunks if their primary(or secondary) extents are not available due to the loss of their underlying devices. So yes, if you are interestedto use the entire space via ASM, going by storage level mirroring is okay.

                   

                  At storage level disk-groups have RAID 10 for +DATA and  +FRA.

                   

                   

                  I am trying to understand the below oracle recommended

                  Use the storage array hardware RAID 1 mirroring protection when possible to reduce the mirroring overhead on the server.

                  Use ASM mirroring redundancy in the absence of a hardware RAID,

                  or when you need host-based volume management functionality, such as mirroring across storage systems.

                  What is need of host-based volume management functionality?


                  As I replied above, you are going to take away now the task from ASM to move the extents and recrete them over the existing disks when their original disks are no longer available. That's the reason, going for the storage level mirroring is a possible alternative.


                  HTH

                  Aman....

                  1 person found this helpful
                  • 6. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                    JuanM

                    ivw wrote:

                     

                    Dear Experts,

                     

                    Is it advisable to have ASM normal redundancy if storage already have RAID 10 .

                     

                    At storage level disk-groups have RAID 10 for +DATA and  +FRA.

                     

                     

                    I am trying to understand the below oracle recommended

                    Use the storage array hardware RAID 1 mirroring protection when possible to reduce the mirroring overhead on the server.

                    Use ASM mirroring redundancy in the absence of a hardware RAID,

                    or when you need host-based volume management functionality, such as mirroring across storage systems.

                    What is need of host-based volume management functionality?



                    Thanks & Regards,

                    ivw

                     

                    Mmmmmm, IMHO, the answer is...no!

                     

                    RAID 10 is mirroring and stripping (hardware level),

                    ASM with normal/high redundancy is stripping and mirroring (ASM file level).

                     

                    In my point of view you are doing twice the "same" configuration/work.

                    Also, that's why oracle gives to us the option "Redundancy External".

                     

                    If you have configured RAID 10 the best option is using ASM without redundancy (external). At this way, as Aman.... said, -ASM striping is inevitable- but does less work.

                     

                    Regards,

                    Juan M

                    1 person found this helpful
                    • 7. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                      Dude!

                      What ASM redundancy and RAID redundancy have in common is redundancy, but how it is accomplished is fundamentally different. Comparing RAID with ASM redundancy is comparing apples and oranges. ASM is not RAID. RAID redundancy mirrors complete disks. ASM provides file based redundancy, using free disk space available on any device that is a failgroup within the ASM diskgroup.

                       

                      ASM unlike RAID knows specifically about Oracle files using appropriate strip sizes for best performance. You can also resize ASM diskgroups and add remove or add devices while the diskgroup is online. RAID is not as versatile and you will have to erase a RAID volume in case you need to reconfigure the volume.

                       

                      Regarding your quote, Oracle does not recommend anything and only shows you what to use depending on your storage requirement. If you can afford it, you can combine RAID and ASM data mirroring to have the best of all worlds, but is an expensive solution because you require twice the amount of disk space for data redundancy than absolutely necessary. Whether you use ASM or RAID redundancy or both is your call.

                      1 person found this helpful
                      • 9. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                        Pini Dibask

                        Hi,

                        I definitely agree with the above comments but I'd like to expand a bit regarding ASM Striping & Mirroring capabilities

                         

                        Oracle ASM provides striping and mirroring capabilities that are similar to RAID 10; however, Oracle ASM doesn't behave exactly as RAID and it can be even smarter due to the fact that it's aware of the different Oracle Database file types. So it can stripe data differently for different file types, while traditional RAID stripes at the block level aren't aware of the different Oracle Database file types. Oracle ASM is also more flexible in terms of mirroring, because it allows different types of mirroring for different files.

                         

                        Striping

                         

                        The goal of striping is to maximize the storage subsystem throughput by balancing the I/O load across several disks, which results in a better performance. By doing so, the I/O latency will be reduced because balancing removes bottleneck from one specific disk.

                         

                        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).

                         

                        Oracle ASM writes in a round-robin fashion across the disks in the disk group—this is why small disks will be filled up faster than large disks, which can cause more frequent rebalance operations. Therefore, a known best practice is to use disks with the same characteristics (such as identical size and performance).

                         

                        Mirroring

                         

                        Oracle ASM mirrors the data based on file extents. Each file extent contains one or more allocation units. Oracle ASM allows us to choose, for each Oracle ASM disk group, the desired redundancy level. We can choose to work with the following:

                         

                        • Normal redundancy: Each file extent has a single copy (also called two-way mirroring).
                        • High redundancy: Each file extent has two copies (also called three-way mirroring).
                        • External redundancy (no mirroring).

                         

                        Moreover, in addition to the ability to configure redundancy level per disk group, we can set the redundancy level for each specific file using Oracle ASM templates, which are another great advantage of Oracle ASM.

                         

                        Oracle ASM mirrors copies of file extents in separate failure groups so that if all the disks in a failure group are lost, our database will continue to function properly because there are copies of the file extents in the other failure group or failure groups. Obviously, if you choose to work with external redundancy, there will be no failure groups in the Oracle ASM disk group. The external redundancy option is commonly used in environments that use storage solutions that already take care of the protection of and the distribution of their data across multiple disks using RAID.  The most common RAID options for Oracle Database are RAID 1+0 (also called RAID 10) and RAID 5. Both provide data protection and striping across disks. In RAID 10, each separate set of disks (usually pairs) is mirrored individually and striping occurs on top of the mirrored sets of disks. RAID 5 distributes the data blocks as well as the parity blocks across all disks. The parity block can be used upon a disk failure for calculating the missing data stripe.  RAID 10 is considered to be the best RAID option for Oracle Database in terms of performance.

                         

                        Figure 1 contrasts external redundancy with no Oracle ASM mirroring, normal two-way mirroring provided by Oracle ASM, and high-redundancy three-way mirroring provided by Oracle ASM. Each square within the disks represents an Oracle ASM file extent.

                         

                        f1.png

                        Figure 1. Mirroring choices with Oracle ASM


                        This info is taken from my article: Verifying I/O Activity Balance Across Disks in ASM

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                        • 11. Re: Is it advisable to have ASM normal redundancy if storage already have RAID 10
                          Dude!

                          I wouldn't compare ASM to RAID because there is no resemblance apart form data striping and redundancy, but even how it is done is fundamentally different. RAID mirrors whole disks and stripes among disks, whereas ASM mirrors individual files using free disk space between ASM failure groups, and by default, every ASM disks is also a failure group. ASM compared to RAID is capacity driven and automatically re-balances data to achieve the desired redundancy when disks are added or removed, even while the data is online. RAID on the contrary does not allow the resizing of a RAID volume without destroying the data. RAID 5 is a cost/benefit factor that provides more capacity over RAID 10 and can provide better read (not write) performance than RAID 10. However, rebuilding a RAID 5 volume in case a device needs to be replaced takes a very long time and if another drive fails during the procedure, all data is lost.