ASM Volumes and DiskGroups

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    • #1909
      [email protected]


      I have a 2Node Oracle RAC Setup(10gR2). ASM Volumes were configured for 2 disk groups as follows, during the installation:

      /dev/sdb2 : VOL1

      /dev/sdb3 : VOL2

      /dev/sdb4 : VOL3

      ORCL_DATA1 : VOL1 & VOL2


      I have some basic doubts about ASM and Database Groups.

      1) I run the foll commands to know/query the ASM Volumes and devices

      # /etc/init.d/oracleasm querydisk /dev/sdb2

      # /etc/init.d/oracleasm listdisks

      # ls -al /dev/oracleasm/disks/

      Can I also get the ‘Disk Group’ information in a similar manner from ASM? eg: What are the disk group names and what vol’s/devices form the diskgroup.

      Currently I am run the below query to get this information

      select, from v$asm_diskgroup d, v$asm_disk e where d.group_number=e.group_number;

      2) Can my database have multiple data groups?

      eg: ORCL_DATA1 (VOL1 & VOL2) and ORCL_DATA2 (VOL3 & VOL4)

      3) Can multiple datagroups share the same Flash Recovery Area?

      eg: ORCL_DATA1 & ORCL_DATA2 have the same Flash Recovery Area (FLASH_RECOVERY_AREA (VOL5 & VOL6)

      4) Can disk groups span across databases?

      5) When I create/alter tables, and if I have two data groups (ORCL_DATA1 & ORCL_DATA2) in the database, do I know where the information is being written or can I provide this information somewhere?

      6) If my database contains multiple disk groups, and incase I wish to rollback the database to a previous good instant of time, can I just rollback some disk groups in the database or ‘ALL’ the diskgroups will have to be rolledback to maintain consistency.

      I am working on RAC as a user and not very clear on the underlying aspects of databases etc. Some of the questions above may sound flimsy.

      Any advise/suggestion is appreciated.


    • #2085
      Amit Bansal

      1. There is no asm command to find the devices part of particular diskgroup. You can use the query to find the diskgroup devices.

      2. Yes, you can have multiple diskgroups

      3. No, you can allocate only one diskgroup to FRA.

      4. Yes, you can have multiple databases using same diskgroup

      5. I cant answer this. You need to read Database Concepts and Admin guide.

      6. No. Can’t be done.

      Deepika , I think it would be better to get a DBA for managing your site as RAC DB’s are much complex then single instance databases on filesystem.

    • #2086
      [email protected]

      Thanks Amit for your reply.

      I am working for a company that makes protection software and we are planning to extend it to support RAC.

      Yes, we do realize that RAC Databases are complex and we therefore are also getting in touch with a DBA. These were some of the preliminary doubts that I had.

      Thanks anyways for your response.

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