DVD writer replacement

[laurentlaur]

I have to replace the defective DVD writer on my laptop and I don't know what product to buy.
The original device is HL-DT-ST DVDRAM GSA-T20L from LG, but I can't get one. So I must find an equivalent.
My laptop is an HP Compaq 6720s.
How can I be sure what DVD writer will work on it?

 

[pip22]

http://h20000.www2.hp.com/bizsuppor...21957&prodSeriesId=3442832&objectID=c01884059

And the drive is available here: http://www.google.com/products/cata...a=X&ei=6sSpTqXLOsWWiALkoejwCg&ved=0CFkQ8wIwAw