L521x supports sata3 ??

from the post http://en.community.dell.com/support-forums/laptop/f/3518/p/19469159/20359261.aspx I had the idea that the L521x supports sata3. I replaced the harddisk with a Samsung evo 840 SATA3 SSD HD.

this is what I get 

$ dmesg | grep -i sata | grep 'link up'
[ 1.726388] ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 2.062740] ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 2.383073] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)

So the Samsung is either ata1 or ata2. ata3 is probably the dvd. Am I doing something wrong? Will an upgrade with a caddy http://hddcaddy.eu/2013/06/19/dell-xps-15z-l521x-15-hdd-caddy/ work if I use the ata3 port? I already chose a sata3 sdd based on the information provided by a dell employee. So it would be nice if I could get an answer to this one.

greets,
Henry