This is more of a sanity check and solicitation of the prior experiences with the similar migration scenarios.
I am planning a migration path from NW 6.5SP8 to OES11 and from the training manuals and various online posts it looks like the following approach of gradually phasing out NW servers should work:
1. add r/w replica on a new OES 11 server (and remove a r/w replica on one old NW server, at this point we will have eDir 8.8SP5 on NW and eDir 8.8SP6 on OES 11 in the replication ring)
2. add a r/w replica on another OES 11 server (...and remove another old r/w replica on a NW server)
3. add another r/w replica on a new OES 11 server and promote it to the master replica
4. make sure there are no other NW servers left running (all file, print, CA, SLP DA, timesync services are running on OES 11 at this point)
5. remove the last r/w replica on the old NW server (... and remove the last NW server from the tree)
Does this sound right? I don't see this specific scenario described in the Upgrade, Migration or Best Practices guides.
BONUS question: what are the advantages of using the migedir utility instead of just adding a replica on the OES 11 server (when the eDir versions are close enough on NW and OES)?