How A Disk is Discovered

When an Oracle ASM instance is initialized, Oracle ASM discovers and examines the contents of all of the disks that are in the paths that you designated with values in the ASM_DISKSTRING initialization parameter.

Disk discovery also occurs when you:

• Run the following SQL statements

  • Mount a disk group with ALTER DISKGROUP MOUNT

  • Online a disk with ALTER DISKGROUP ONLINE DISK

  • Add a disk to a disk group with CREATE or ALTER DISKGROUP...ADD DISK

  • Resize a disk in a disk group with ALTER DISKGROUP...RESIZE DISK

  • Query with SELECT FROM V$ASM_DISKGROUP or V$ASM_DISK views

• Run Oracle ASM Configuration Assistant (ASMCA) operations or ASMCMD commands that perform the same operations as the SQL statements previously listed

After Oracle ASM successfully discovers a disk, the disk appears in the V$ASM_DISK view. Disks that belong to a disk group, that is, disks that have a disk group name in the disk header, show a header status of MEMBER. Disks that were discovered, but that have not yet been assigned to a disk group, have a status of either CANDIDATE or PROVISIONED. Disks that previously belonged to a disk group and were dropped cleanly from the disk group have a status of FORMER.

The PROVISIONED status implies that an additional platform-specific action has been taken by an administrator to make the disk available for Oracle ASM. For example, on Windows computers, the administrator might have used asmtool or asmtoolg to stamp the disk with a header. For example, on Linux computers, the administrator might have used Oracle ASM Filter Driver or ASMLIB to prepare the disk for Oracle ASM.

Example 4-10 shows a SQL query on V$ASM_DISK that displays the header status of a group of disks.

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

NAME      HEADER_STATUS PATH
--------- ------------- ---------------------
          FORMER        /devices/disk02
          FORMER        /devices/disk01
          CANDIDATE     /devices/disk07
DISK06    MEMBER        /devices/disk06
DISK05    MEMBER        /devices/disk05
DISK04    MEMBER        /devices/disk04
DISK03    MEMBER        /devices/disk03
7 rows selected.