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IOCTL_VOLUME_READ_PLEX IOCTL (ntddvol.h)

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Performs a read on a specific plex of a volume. Because all plexes are identical, the volume manager can retrieve data from any of a volume's plexes during a normal read operation. The volume manager spreads reads among a volume's plexes, to balance the I/O load on the physical media and to maximize read performance.

If, however, an application or kernel-mode component must read data from a particular plex instead of letting the volume manager pick one, it can use this IOCTL to do so.

Major code

IRP_MJ_DEVICE_CONTROL

Input buffer

Caller inserts the VOLUME_READ_PLEX_INPUT structure, containing the logical offset, at the beginning of the buffer at Irp->AssociatedIrp.SystemBuffer.

Input buffer length

Parameters.DeviceIoControl.InputBufferLength in the I/O stack location of the IRP indicates the size, in bytes, of the input buffer, which must be greater than or equal to the value of sizeof(VOLUME_READ_PLEX_INPUT).

Output buffer

Like IRP_MJ_READ, this IOCTL stores the read data in the memory buffer passed as a memory descriptor list (MDL) in the Irp->MdlAddress field.

Output buffer length

The length of the buffer.

Status block

If the operation is successful, the volume manager sets the Status field to STATUS_SUCCESS.

The VOLUME_READ_PLEX_INPUT structure at Irp->AssociatedIrp.SystemBuffer has a Length member that must be aligned on a 512-byte boundary. If Length does not have the proper alignment, the operation fails and the volume manager sets the Status field to VKE_EINVAL.

Requirements

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

See also

VOLUME_READ_PLEX_INPUT