Find Candidate disk for creating diskgroup in Oracle ASM

ASM successfully discovers a disk, the disk appears in the V$ASM_DISK.

Disk has different header_status column in V$ASM_DISK view
MEMBER: Disks that assigned to a disk group.
CANDIDATE or PROVISIONED: Disk that been discovered but not assigned to any disk-group. PROVISIONED status an additional platform-specific action has been taken by an administrator to make the disk available.
FORMER: Disks that previously belonged to a disk group and were dropped cleanly from the disk group.


SELECT name, header_status, path FROM V$ASM_DISK WHERE path LIKE '/devices/disk0%';

NAME      HEADER_STATUS PATH
--------- ------------- ---------------------
          FORMER        /devices/disk01
          FORMER        /devices/disk02
DISK03    MEMBER        /devices/disk03
DISK04    MEMBER        /devices/disk04
DISK05    MEMBER        /devices/disk05
          CANDIDATE     /devices/disk07

Note:
–Disk Managed by Oracle such a disk appears in the V$ASM_DISK view with
a status of FOREIGN. For add must use FORCE keyword.
–Member disk are also added by FORCE, if disk is not part of currently mounted diskgroup

ASM_DISKSTRING initialization parameter is an operating system–dependent value that Oracle ASM uses to limit the set of paths that the discovery process uses to search for disks.