Mounting Disk Groups Using the FORCE Option

Oracle ASM provides a MOUNT FORCE option with ALTER DISKGROUP to enable Oracle ASM disk groups to be mounted in normal or high redundancy modes even though some Oracle ASM disks may be unavailable to the disk group at mount time. The default behavior without the FORCE option is to fail to mount a disk group that has damaged or missing disks.

The MOUNT FORCE option is useful in situations where a disk is temporarily unavailable and you want to mount the disk group with reduced redundancy while you correct the situation that caused the outage.

To successfully mount with the MOUNT FORCE option, Oracle ASM must be able to find at least one copy of the extents for all of the files in the disk group. In this case, Oracle ASM can successfully mount the disk group, but with potentially reduced redundancy.

The disks that Oracle ASM cannot access are placed in an offline mode. Oracle ASM then begins timing the period that these disks are in an offline mode. If the disk offline time period exceeds the timer threshold set by DISK_REPAIR_TIME disk group attribute, then those disks are permanently dropped from the disk group. You can change the offline timer after a disk is put in an offline state by using the ALTER DISKGROUP OFFLINE statement. For more information about setting the DISK_REPAIR_TIME disk group attribute, see "Oracle ASM Fast Mirror Resync".

In clustered Oracle ASM environments, if an Oracle ASM instance is not the first instance to mount the disk group, then using the MOUNT FORCE statement fails. This is because the disks have been accessed by another instance and the disks are not locally accessible.

If all disks are available, then using the FORCE option causes the MOUNT command to fail. This discourages unnecessary and improper use of the feature.

The following example shows how to use the FORCE option to force the mount of the data1 disk group:

SQL> ALTER DISKGROUP data1 MOUNT FORCE;