The NTMS_ALLOCATION_INFORMATION structure contains information about the source media pool from which a medium was taken.

 typedef struct _NTMS_ALLOCATION_INFORMATION {
   DWORD dwSize;
   byte* lpReserved;
   NTMS_GUID AllocatedFrom;
 } NTMS_ALLOCATION_INFORMATION,
  *LPNTMS_ALLOCATION_INFORMATION;

dwSize: The size, in bytes, of the structure.

lpReserved: Unused. This value MUST be NULL and MUST be ignored on receipt.

AllocatedFrom: The GUID of the media source (that is, an import pool or any other user-defined pool).