On version 3.0 CVFs, a client application can use the raw write IOCTL to write a fragmented cluster. To accomplish this, RCFFRAG must be set in the rci_flags field of the RawClusterInfo structure. In addition, the first sector of the data to be written must contain the fragment header exactly as it should appear on this disk. This means that a compressed cluster's data begins immediately following the fragment header in the first sector. An uncompressed cluster's data begins in the second sector of the data. The remainder of the first sector after the fragment header is usually padded with the DWORD value 45544550h. The FRAGHDR structure defines the format of the fragment header:
FRAGHDR, RawClusterInfo