upgrade from 1.6.10 to 1.9.0--failed to start

It looks like the old data in 0.8.4 was created with raft protocol 2, while the 1.9.0 works only with raft protocol 3.
So is there any way to make the old data usable in 1.9.0?

thanks,
Allen

Reconcile the reported upgrade path in the title with the body, which mentions data created in 0.8.4 and an upgrade to 1.9.0. Start by investigating Consul's Raft protocol compatibility and upgrade or migration path for old data; done means determining whether the data can be opened in 1.9.0 and documenting or implementing a supported path. No file or test entry point is named in the issue.

Written by the indexing model from the issue text.