windows 7 - How to mirror multiple sources to a single destination?

I have multiple 2-3TB drives inside and connected to my working PC. The data I want to backup on each system lies in the folder "digitalized" (photos, time-lapse, etc).

I have a NAS (PC with 8 drives in a JBOD array) with 9TB free.

I would like to mirror each of my source drives to my backup PC:

d:\digitalized -> b:\
e:\digitalized -> b:\
f:\digitalized -> b:\
g:\digitalized -> b:\
h:\digitalized -> b:\

I manually copied of all source drives to the NAS (which took about 4 days). (Full-size here: http://i.imgur.com/41YVQjz.jpg - 2 million baby jpegs, eeeeeh!)

Now, one month later, a lot has been deleted, edited and added on the source drives so I need to synchronize everything.

I also have a kazillion tiny useless catalog preview files (from Lightroom) which I would like to ignore. Here is what I have come up with so far:

robocopy X:\DiGiTaLiZeD B:\ *.* /zb /e /purge /eta /xd *.lrdata /xf *.lrprev

Replace 'X' with each drive letter and repeat. Put into a batch file which runs whenever NAS is pingable.

Problem:

Each time robocopy runs, /purge sees that 75% of the files located on dest do NOT exist on source (D:) because that data is from E:, F:, etc., so it begins to delete everything else! BAD ROBOCOPY BAD! :(

Any clever ideas? It doesn't have to involve robocopy but I thought it would be the simplest since it's included with Windows.

Answer

Instead of copying your many source drives to the root directory of B:\, create sub directories (B:\FromD\, B:\FromE\ etc) and use robocopy to mirror each source to the sub directories on the B: drive.