Mac mini server - external hard drives enclosure file transfer speed

Hi guys!

I wanted to increase the file transfer speed and storage capacity of my Mac mini so I bought an external hard drives enclosure. The one I bought is : http://www.icydock.com/goods.php?id=219

Mac mini's built-in hard drives transfer file at 60Mb/s (write and read) and I wanted to get way better file transfer speed so I bought an SSD that is going to be in the enclosure with another HDD of 3Tb for archiving my files. The enclosure is connected by USB3.0 (5Gb/s) to the Mac mini.

[SSD -> Files I open every day] - Speed around 550Mb/s write and 500Mb/s read

[HDD -> Archives, files that I won't open very often] - Speed around 150Mb/s write and 150Mb/s read

So I did some benchmarks on my new setup, and the speed isn't really what I expected. The max file transfer speed I reached is about 100Mb/s in writing on the external SSD plugged to the mac mini. This transfer has been made from an iMac 21" 2011 with an SSD (with almost same speed in writing/reading than the one in the enclosure) so that's quite disappointing.

Is it possible that the Mac has a "file transfer speed limit" set somewhere? Or whatever else that could affect that?

More informations about my setup:

Mac Mini server 2012 - 2 Tb RAID 1 - Mac OSX 10.9.5

iMac 21" 2011 - Crucial SSD 275Gb - Mac OSX 10.9.4

IcyDock external enclosure - 4 bays, USB3 5Gb/s

- Red WD HDD 3To

- Crucial SSD 1To

Whole internal network in Gigabit ethernet

Thanks!