How to Identify the ASM Device from ASMLib

In Linux, ASMLib provides the wrapper for managing the ASM disks. To identify the underlying physical device that the ASM disk point to, you can use the oracleasm querydisk command. In this blog, we will teach you how to identify the ASM device from ASMLib.

The querydisk option will list the major and minor numbers that can be used to match the physical device.

The following example was run on a virtual server hosting ASM and an Oracle database.

[root@oraclevm ~]# oracleasm listdisks
DATA1
[root@oraclevm ~]# oracleasm querydisk -d DATA1
Disk "DATA1" is a valid ASM disk on device [8,17]
[root@oraclevm ~]# ls -ltr /dev/sd*
brw-rw----. 1 root disk 8, 0 Dec 14 18:18 /dev/sda
brw-rw----. 1 root disk 8, 2 Dec 14 18:18 /dev/sda2
brw-rw----. 1 root disk 8, 1 Dec 14 18:18 /dev/sda1
brw-rw----. 1 root disk 8, 16 Dec 14 18:18 /dev/sdb
brw-rw----. 1 root disk 8, 17 Dec 14 18:18 /dev/sdb1
[root@oraclevm ~]#

In the above example, DATA1 disk is pointing to the /dev/sdb1.  The major 8 is block based and refers to SCSI disk devices type.

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Identifying the Underlying Physical Device for an ASMLib ASM Disk

When Oracle ASM uses ASMLib for disk management on Linux, ASMLib maintains labels for ASM devices and provides utilities to work with them. You may find it useful to determine which physical block device corresponds to an ASM disk that is managed through ASMLib.

Oracle’s oracleasm utility includes commands that let you inspect the mapping between ASM labels and the underlying device nodes:

1. List ASM disks managed by ASMLib.
   Run oracleasm listdisks to show the names of ASM disks that ASMLib knows about. This gives you the labels assigned to each ASM disk.
2. Query a specific ASM disk.
   Use oracleasm querydisk -d <ASM_LABEL> to retrieve information about the ASM disk named <ASM_LABEL>. The output includes major and minor device numbers for the device associated with that ASM label.
3. Match the major/minor numbers to a physical device.
   Once you have the major and minor numbers, list block devices on the host with a command such as ls -l /dev/sd*. The major and minor numbers shown in the ls output help you identify which /dev/<name> node corresponds to the ASM device. 

Using these steps lets you trace an ASMLib-managed ASM disk label to the actual storage device path on the host operating system. This approach works whether ASM devices are partitioned or use whole disks, and it relies on standard ASMLib utilities that are included when ASMLib is installed and configured.

Get started today and check out our Solutions Brief on how to uncomplicate your Oracle data!

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