How to Resolve ASM Disks Not Visible

Requirements for Disk Discovery

There're several requirements for disks to be discovered:

1. Right Device Type

For 11g or later, only block devices leading by letter b in permission notation are acceptable, any others device types, such as character devices, symbolic links (leading by letter l) and pseudo devices are not ASM candidates.

Please see an example of block device in the following content.

2. Proper Permission

If you plan to use grid to install grid infrastructure, then the owner of disks should be grid:asmadmin, not root:root.

[root@primary01 ~]# ll /dev/sdb1
brw-rw---- 1 grid asmadmin 8, 17 Oct 10 12:58 /dev/sdb1

Either using persistent rule of udev or ASMLib can set the permission properly.

3. Compatible sector size

Since release 12.2, ASM disks have to be compatible with the possible combination of physical and logical sector size of disks. In summary, either 512 or 4K is acceptable.

That is to say, ASM does not accept physical sector sizes larger than 4K. But we can work around the restriction by using the logical sector size instead of physical sector size if you're using ASMLib.

4. Correct discovery path

The default path of disks for ASM to discover is /dev/sd*. You can change the discovery path by clicking on Change Discovery Path in grid infrastructure OUI.

For ASMLib, there're two possible paths where ASM can find disk candidates.

  1. /dev/oracleasm/disks
  2. ORCL:*

You can try above paths one by one.

4 thoughts on “How to Resolve ASM Disks Not Visible”

  1. HI,
    Thanks for this blog.
    But I am facing issue while installing oracle 12.2 grid.
    While selecting ASM disk during installation, it is showing error INS 30515.
    Cause – Insufficient space available in the selected Disks. At least, 38,728 MB of free space is required.
    Action – Choose additional disks such that the total size should be at least 38,728 MB

    But i have given 30gb space ,.

    Need your help.

    OS – OEL 7.8
    GRID – Oracle 12.2
    Thanks,
    Kumar

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