Hi,
if you want to install a RHEL8 or RHEL9 server with the same domain name, the recommended procedure would be to install a RHEL8 replica from your RHEL7 server, then a RHEL9 replica from your RHEL8 server.
You can check this documentation:
- Migrating your IdM environment from RHEL 7 servers to RHEL 8 servers [1]
- Migrating your IdM environment from RHEL 8 servers to RHEL 9 servers [2]
ipa migrate-ds is used when the new domain name is different from the old one and does not migrate all the data (only users and groups are migrated, not HBAC rules, sudo rules etc...). On the contrary, installation of a replica does not lose any data. And you don't need to worry about the SIDs.
HTH,
flo