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The Oracle 11gR2 Automatic Storage Managament Administrator's Guide says:

When Oracle ASM allocates an extent for a mirrored file, Oracle ASM allocates a primary copy and a mirror copy. Oracle ASM chooses the disk on which to store the mirror copy in a different failure group than the primary copy.

It also says:

If you omit the failure group specification, then Oracle ASM automatically places each disk into its own failure group, except for disk groups containing disks on Oracle Exadata cells.

My question is for the following scenario how ASM will create failure groups:

  1. In my server when there is one disk controller and one physical hard disk having many logical volumes and created disk groups.

  2. When server is having two controller card and two or more hard disks with logical volumes created and used for diskgroups.

My main question is, I want to understand how this ASM decides failgroups? Please some one can guide

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  • My question is for the following scenario how ASM will create failuregroups: 1. In my server when there is one disk controller and one physical hard disk having many logical volumes and created disk groups. 2. When server is having two controller card and two or more hard disks with logical volumes created and used for diskgroups.
    – user3134198
    Jan 7 '14 at 11:02
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As the official documentation says, unless you specify failure groups explicitly, ASM will place each disk into its own failure group (it doesn't have any knowledge about your HW infrastructure).

Note that Oracle doesn't recommend using an OS LVM with ASM.

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  • Sorry but I am not able to understand what does it mean by "Each disk is placed into its own failure group"? Please can you explain me more about that, thanks.
    – user3134198
    Jan 9 '14 at 10:17
  • @user3134198, it means that you have a separate failure group for each asm disk. If, for example, your asm diskgroup contains 3 asm disks, you have 3 failure groups. Note that failure groups are relevant only when asm mirroring is used (i.e. for normal and high redundancy) and nowadays asm seems to be used mainly with external redundancy. For more detailed information check the official documentation.
    – Dimitre Radoulov
    Jan 9 '14 at 10:54
  • It is very simple. Oracle doesn't know what your hardware configuration is. It can only see ASM Disks. Unless you tell it otherwise, it will create one failure group for every ASM Disk it can see.
    – Andrew Brennan
    Apr 8 '14 at 12:14

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