No one blinks at multiple 2-year stints, especially if they were spent at smallish companies (< 500 employees). Spending 2 years usually means you went through at least 2 performance review cycles, accomplished or delivered something and are looking for something new to work on. At smaller companies it's not always possible to change group, so it's logical that you might look to change your job instead.

My own work history so far has been similar - 3 jobs lasting between 1.5 and 2.5 years, and I'm now currently on my 4th. It's never been brought up as an issue in interviews.