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.

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.

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.