Colin, if I remember correctly, you first ran Tarsnap servers on Ubuntu before you made FreeBSD work on EC2. At what point were you confident enough to switch to FreeBSD?
I think cc1.4xlarge was the first instance I ran the Tarsnap service on. Being HVM made me far more confident -- PV dramatically increases the risk of VM/paging bugs, which is exactly the way to get silent data corruption.
So... I'd have to check my notes to be sure but I think fall 2011?
