just wanted to let you know that i found a cheap SATA port multiplier working perfectly with my GoFlex Net.
Bought this one on ebay: http://www.ebay.ca/itm/ws/eBayISAPI.dll?ViewItem&item=271057098889#ht_3495wt_1271
and attached 4 SATA HDDs to it...
perfectly working with archlinux!!! just in case anyone wants to attach more than 2 SATA disks

cheers