6 Replies Latest reply: Nov 12, 2013 12:35 PM by user130038 RSS

    Size of LUNs for ASM

    user130038

           Hi there

       

      ENV: Oracle 10g R2 EE on ADM, RHEL 5.8 64bit

       

      Is there a difference performance wise if ASM gets two LUNs of 1.7TB (DATA) and 0.6TB (FRA) respectively compared to 17 LUNs of 100GB each (for DATA) and 6 LUNs of 100GB each (for FRA)?

       

      Is there a recommended size from Oracle?

       

      Please advise!

       

      Best regards

        • 1. Re: Size of LUNs for ASM
          srsatya

          Hi,

           

          Please follow this link "http://www.ougn.no/f/601_oracle-asmbestpracticesougn2009-05-27.pdf"

           

          Extract from that document is

           

          What is the best LUN size for ASM?

          There is no generic best size, in most cases the storage team will

          dictate based on their standardized LUN size.

          Communicate the ASM Best Practices and application characteristics

          to the storage team:

          • Need equally sized / performance LUNs
          • Do not use LUNs larger than 2 TB (minimum of 4 MB)
          • The capacity requirement
          • The workload characteristic (random r/w, sequential r/w) & any response time SLA
          • 2. Re: Size of LUNs for ASM
            user130038

            Thank you so much for sharing this information with me!

             

            One question remains unanswered though:

             

            Is there a difference performance wise if ASM gets two LUNs of 1.7TB (DATA) and 0.6TB (FRA) respectively compared to 17 LUNs of 100GB each (for DATA) and 6 LUNs of 100GB each (for FRA)?

             

            We are using "External Redundancy".

             

            Thanks again!

            • 3. Re: Size of LUNs for ASM
              srsatya

              Hi,

               

              Performance wise I dont think it makes any difference because performance depends on SAN & its Cache and all disk's in diskgroup should have similare performance characteristics (interms of disk rpm kind....)...from maintenance point of view, if you have more luns then more maintenance...

              • 4. Re: Size of LUNs for ASM
                srsatya

                Having said that, I will share my personal experience, we had 20 LUN's for DATA diskgroup and 40 LUN's for FRA diskgroup, in FRA diskgroup we used to store Rman bakcup's and archives logs. There was a situation where data diskgroup was running out of space and for various reasons storage team was delaying to provide more storage, then I borrowed two luns from FRA diskgroup (which had enough free space) and added to data diskgroup. When we got new luns for data diskgroup from storage team, then I added them to data and pulled the borrowed LUN's of FRA and added backto FRA diskgroup, you will have such flexibility if you have more lun's.

                • 5. Re: Size of LUNs for ASM
                  Levi Pereira

                  Is there a difference performance wise if ASM gets two LUNs of 1.7TB (DATA) and 0.6TB (FRA) respectively compared to 17 LUNs of 100GB each (for DATA) and 6 LUNs of 100GB each (for FRA)?

                   

                   

                  Diskgroup above 2TB I recommend creating LUNs on the size of up to 10% of the total size of the ARRAY.

                  You can explore all available controllers performing balancing the LUNS on the controllers.


                   

                  This will help with future maintenance as placing new disks or removing disk to save unused space.

                   

                  Oracle ASM data distribution policy is capacity-based. Ensure that Oracle ASM disks in a disk group have the same capacity to maintain balance.

                  If in future you need to add new LUNS on Diskgroup you should keep in mind that if you created a 500GB LUN then you must add a new LUN of 500GB.

                   

                  I recommend 10% based on my own experience, I do not mean that this is the optimal for your environment, each environment should be analyzed.


                   

                  Is there a recommended size from Oracle?

                  Oracle Support  notes:


                  How to Prepare Storage for ASM [ID 452924.1]

                  Lun Size And Performance Impact With Asm [ID 373242.1]

                   



                  • 6. Re: Size of LUNs for ASM
                    user130038

                    Thank you so much both!

                     

                    Best regards