For a while the 2.0 development branch was using a different storage file format than 1.x, which required migrating your time series data.

But by the 2.0 Release Candidate that was reverted so that it will use the same file format as 1.x, and the 2.0 functionality was backported onto that, so the upgrade path for 1.x to 2.0 is much simpler now than it was going to be.