4 Replies Latest reply: Jun 17, 2012 1:57 PM by scottjhn RSS

    which raid should be used on asm oracle rac11g

    834639
      Hi,

      As we are going to upgrade our system to new hardware and also the software. We are implementing oracle rac 11g with asm and using a HARDWARE raid not software.

      Some people suggest me to use raid 6 following are the questions I am searching for:

      1. What does raid 6 means and how does it works with asm?

      2. what will be the combination used to get optimal performance from storage e.g

      RAID 1+0 = redolog

      RAID 5= Archvielogs

      like this.

      Thank you so much for helping me.

      Kind Regards,

      Adnan Hamdus Salam
        • 1. Re: which raid should be used on asm oracle rac11g
          Billy~Verreynne
          Oracle recommends SAME - Stripe And Mirror Everything.

          ASM itself supports striping of a diskgroup's contents. So if you have 3 disks in an external redundancy diskgroup, then data written to that diskgroup will be striped across all 3 disks in that diskgroup. This is fixed and default behaviour.

          ASM provides 2 redundancy options (in addition to no redundancy/external redundancy). It provides 2-way (normal redundancy) and 3-way (high redundancy) mirroring.

          So in effect, ASM supports SAME.

          ASM does not support RAID5, RAID6 and other RAID level. You cannot implement such a RAID level in ASM.

          ASM can however use RAID5 or RAID6 disks. And because these are already configured as redundant, you can tell ASM not to mirror the contents of the disksgroup that resides on RAID5 disks.

          E.g. you can create diskgroup DATA1 as an externally redundant diskgroup and add 3 RAID5 disks into the group. However, ASM will automatically stripe the data of the DATA1 diskgroup, across all 3 RAID5 disks.

          So as for what RAID level to use. You have 3 choices in ASM. External redundancy, normal redundancy or high redundancy. The one to use depends on how your underlying storage system looks like, and the level of redundancy you want.
          • 2. Re: which raid should be used on asm oracle rac11g
            834639
            Hi Billy,

            Thank you for your response.

            As you said "ASM can however use RAID5 or RAID6 disks. And because these are already configured as redundant, you can tell ASM not to mirror the contents of the disksgroup that resides on RAID5 disks".

            Does it apply to RAID 6 regarding mirroring of ASM disks?


            Thank you so much for clearing my concept.

            Thank you for your cooperation.

            Kind regards,

            Adnan Hamdus Salam.
            • 3. Re: which raid should be used on asm oracle rac11g
              Billy~Verreynne
              adnan wrote:

              As you said "ASM can however use RAID5 or RAID6 disks. And because these are already configured as redundant, you can tell ASM not to mirror the contents of the disksgroup that resides on RAID5 disks".
              Correct. You simply define that diskgroup as being externally redundant. ASM will therefore not mirror that diskgroup.
              Does it apply to RAID 6 regarding mirroring of ASM disks?
              It applies to all RAID disks. You can use any RAID disks - create an ASM diskgroup for those disks and tell ASM not to mirror it, as that diskgroup resides on externally redundant disks.

              ASM does not know what RAID levels a disk is. It only knows that it is a disk that it can use. The HOW TO USE, you need to explicitly tell ASM. You need to tell ASM whether you want to use that disk as part of externally redundant diskgroup, a normal redundant diskgroup, or a highly redundant diskgroup.

              The disk may not even be RAID'ed. It could be a plain local hard SATA/SAS disk. No RAID. And you can tell ASM t create an externally redundant diskgroup using the disk. ASM then leaves the redundancy for that disk in your hands and up to the underlying storage architecture.

              If there is no RAID and the SATA/SAS disk fail.. bye-bye all data on that disk. Not ASM's problem.

              If that disk is part of a RAID6 set and it fails.. not ASM's problem. You and the underlying storage system need to manage redundancy and fix the RAID for that disk.

              Only when you tell ASM that the diskgroup is redundant, then it will mirror. And expect you to supply sufficient disks for it to maintain a 2-way or 3-way mirror for that diskgroup, as per your diskgroup configuration.