Backup using xcopy

Hello all, I have recently purchased a 1tb mybook, and I have been very impressed so far. The unit was purchased for our work network, we currently have several backup units some are USB units and some are NAS units. We use a simple bat file to backup all of our data, the command is as follows XCOPY *.* B:\ /d /e /v /c /i /f /h /y This backup command has worked faultlessly for many many years and works perfectly on all of our current nas drives. In theory the bat file will only move data that has changed since lance backup, that is the /d attribute. However whenever I run a backup it always does a full backup onto this unit, even though the data is in tact. Does anyone know a way to stop the nas drive from doing this? thanks

Dear _Spud_

Switch /D does not work as intended or claimed. Microsoft strikes again!

Switch /M  However, does the job fine for me. Only copies files that have changed or new files.

Batch file is invoked weekly from Scheduled Tasks.

Note the target M:/ Drive below points to my NAS MyBookWorld. 

Switch /M   COPIES ONLY FILES WITH THE ARCHIVE ATTRIBUTE SET, AND
TURNS OFF THE ARCHIVE ATTRIBUTE. THIS SWITCH EFFECTIVELY ONLY COPIES
SOURCE FILES THAT HAVE CHANGED OR NEW FILES AND DIRECTORIES CREATED
 SINCE THIS BATCH FILE WAS LAST RUN

Copy of my Batch File …

ECHO OFF
ECHO .
TITLE BACKUP LAPTOP DATA DIRECTORIES TO MYBOOKWORLD/PUBLIC
ECHO **************************************************************************
ECHO NEW BACKUP BATCH FILE CREATED 16 JULY08 USING XCOPY WITH THE “/M” SWITCH
ECHO /M - COPIES ONLY FILES WITH THE ARCHIVE ATTRIBUTE SET, AND
ECHO      TURNS OFF THE ARCHIVE ATTRIBUTE. THIS SWITCH EFFECTIVELY ONLY COPIES
ECHO      SOURCE FILES THAT HAVE CHANGED OR NEW FILES AND DIRECTORIES CREATED
ECHO      SINCE THIS BATCH FILE WAS LAST RUN
ECHO .
ECHO OTHER SWITCHES USED ARE:
ECHO /S - Copies directories and subdirectories except empty ones.
ECHO /E - Same as /S but includes empty directories. Is /S still required?
ECHO /C - Continues copying even if errors occur.
ECHO /I - If destination does not exist and copying more than one file,
ECHO      assumes that destination must be a directory.
ECHO /R - Overwrites read-only files.
ECHO /Y - Suppresses prompt to confirm overwrite of existing dest. file.
ECHO .
ECHO ************************************************************************** 
ECHO ON
xcopy c:\Data\AA-work M:\Laptop\Data\AA-work /S /E /C /I /R /Y /M

i would love to do something like this keep both of my NAS devices with same data but only understand 75% of this post. any extra help?