IOCTL_VOLUME_ONLINE IOCTL (ntddvol.h)

The IOCTL_VOLUME_ONLINE IOCTL puts the volume in an ONLINE state, which is a state where read and write operations will be executed. The requests are passed down to the physical disk until a subsequent IOCTL_VOLUME_OFFLINE is received.

A common use for IOCTL_VOLUME_ONLINE is a case in which the mount manager automatically puts a new volume in the ONLINE state when the volume arrives, unless that volume is listed in a registry key that is populated by the cluster service. IOCTL_VOLUME_ONLINE is called for removable drives regardless of the NoAutoMount setting in the following registry key:

HKCU\System\CurrentControlSet\Services\Mountmgr\NoAutoMount

But for volumes controlled by NoAutoMount, assigning a drive letter will cause IOCTL_VOLUME_ONLINE to be called.

For volumes that are controlled by the cluster service, IOCTL_VOLUME_ONLINE is sent by the cluster service when the local node owns the volume. The cluster service uses both IOCTL_VOLUME_ONLINE and IOCTL_VOLUME_ONLINE to allow I/O to a disk volume when the disk volume is owned by the local server. Until the cluster service puts the disk volume in an ONLINE state, no I/O is permitted to the disk volume. This prevents disk volume corruption that could result from multiple cluster nodes writing to the same disk volume simultaneously.

Major code

IRP_MJ_DEVICE_CONTROL

Input buffer

None.

Input buffer length

None.

Output buffer

None.

Output buffer length

None.

Status block

The Status member is set to STATUS_SUCCESS.

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows XP.
Header	ntddvol.h (include Ntddvol.h)

See also

IOCTL_VOLUME_OFFLINE