Is it a bad idea to daisy chain to an internet router through an external drive? I'm interested in setting up a wired connection to my router, in order to achieve a faster internet connection than I can get from built-in 802.11n. My 2012 Mac Book Air has only one Thunderbolt 1 port, and that port is in use by an external LaCie HD with two Thunderbolt ports. So I would be connecting to the internet this way:

2012 MacBook Air &gt;
Thunderbolt 1 Cable &gt;
Lacie HD &gt; 
Apple Thunderbolt to Gigabit Ethernet Adapter &gt; 
Fast Cat5E UTP Patch Cable &gt; 
Netgear Router &gt;
cable modem


Will having a hard drive between a laptop and its internet connection impose a significant performance cost?
No, there will be no significant performance loss, if any. The reason is that Thunderbolt is a low-latency, 10Gb/s (minimum) connection, which is far faster than the gigabit speeds you get from the adapter. Thunderbolt will have to wait for your ethernet adapter, not the other way around, which is exactly what you want.

If you're worried about the hard drive taking up some of the performance, keep in mind that the first iteration of Thunderbolt (the one you have) was designed with two lanes. Each device will utilize one of those lanes, and have complete access to dedicated 10Gb/s performance.