Brings a volume online.

Windows Server 2003 and Windows XP:  This control code is not supported for dynamic disks.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,             // handle to device
  IOCTL_VOLUME_ONLINE,          // dwIoControlCode
  NULL,                         // lpInBuffer
  0,                            // nInBufferSize
  NULL,                         // lpOutBuffer
  0,                            // nOutBufferSize
  (LPDWORD) lpBytesReturned,    // number of bytes returned
  (LPOVERLAPPED) lpOverlapped   // OVERLAPPED structure


When a volume is offline, all read, write, and IOCTL requests fail with ERROR_NOT_READY. You cannot take the system or boot volume offline.

When a volume is online, all requests sent to the volume are honored.

When a volume that is online is dismounted, the next call to open the volume causes it to be mounted. Taking the volume offline prevents the dismounted volume from being mounted again.

To take a volume offline, use the IOCTL_VOLUME_OFFLINE control code.

In Windows 8 and Windows Server 2012, this code is supported by the following technologies.

Technology Supported
Server Message Block (SMB) 3.0 protocol No
SMB 3.0 Transparent Failover (TFO) No
SMB 3.0 with Scale-out File Shares (SO) No
Cluster Shared Volume File System (CsvFS) No


Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header winioctl.h (include Windows.h)

See also