9 Replies Latest reply: Nov 1, 2010 7:14 AM by CKPT RSS

    Redo log groups on ASM

    797325
      Hi All

      Is there any difference between creating redo log groups on ASM and creating the same redo log groups on Cluster file system ? if yes , can you please give me an example ?

      Thanks
        • 1. Re: Redo log groups on ASM
          Aman....
          user12302159 wrote:
          Hi All

          Is there any difference between creating redo log groups on ASM and creating the same redo log groups on Cluster file system ? if yes , can you please give me an example ?
          Difference in what way?

          Aman....
          • 2. Re: Redo log groups on ASM
            Catch 22
            ASM is meant to provide data redundancy by physically mirroring individual files. A cluster file system is providing shared access of a file and managing shared I/O requests. Basically. A cluster file system as such does not provide data redundancy or protect from disk failure.

            Edited by: waldorfm on Nov 1, 2010 2:57 AM
            • 3. Re: Redo log groups on ASM
              ergemp
              ASM supports redo log files like cluster filesystems. But as far as I know Oracle strongly recommends to place redo log files on different physical disks than the datafiles and the archivelogs also. So if you are planning to place your redo logs on the ASM maybe it is better to create a seperate ASM diskgroup.

              ASM also has the ability to stripe and mirror the disks under a diskgroup so this functionality also gives you better performance according to the configuration you already have or planning to have. Of course it depends on your cluster disk infrastructure and ASM infrastructure also.

              You should also check the configuration of the storage and the LUN architecture to avoid double stripe issues.
              • 4. Re: Redo log groups on ASM
                Catch 22
                From what I understand, ASM does not mirror disks, it works based on file extents to make sure files meet redundancy needs, even if e.g. a disk of a diskgroup goes bad.
                • 5. Re: Redo log groups on ASM
                  ergemp
                  You can both use striping and mirroring with ASM. You can also give the redundancy and the performance options to the underlying disk subsystem. They are all up to you and your planned configuration. You can find detailed information below.

                  http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/storeman.htm#i1021337
                  • 6. Re: Redo log groups on ASM
                    Centinul
                    What waldorfm is saying is that mirroring is done on the extent level not the disk level as you mentioned. This is also described in the link you posted.
                    Mirroring takes place at the extent level
                    • 7. Re: Redo log groups on ASM
                      rui_catcuddler
                      there is no difference from what you can do other than size and file location for the most part, groups, and number of redo files.

                      Under the hood it's a different story. Extents can be mirrored between failure groups as was mentioned. However, in asm stripe sizes are different for redologs (fine) as opposed to datafiles (coarse). You can control that a little ("maybe") by creating templates and applying templates to the redo logs but that is about it really from what you can do.
                      • 8. Re: Redo log groups on ASM
                        ergemp
                        Sorry for misunderstanding, thats right :) ASM quarantees that the extents are mirrorred if it is configured so. But does not allow you to configure which disks will be used to store the mirror copy of the individual extent (of course if you are using more than 2 disks, otherswise ASM would have no chanche to use the second disk for the extents in the first disk to be mirrored)
                        • 9. Re: Redo log groups on ASM
                          CKPT
                          Hi,
                          you are talking in terms of performance?
                          redo log file is redo log.. you can put either OCFS/ACFS or normal file system.. it depends on your architecture of database.