[Samba] both Samba-4.9.5 AD DC upgrade to Samba current (4.22.*) - questions

[Franta Hanzlík]

We are preparing to upgrade our two Samba AD DCs during this school 
holidays. Both current DCs are x86_64 VMs with Samba 4.9.5, AD schema 
= 47 (Server 2008R2), there is one AD domain.
We expect to upgrade to Samba 4.20.* or 4.22.* and AD schema to current
Server 2019 or 2022.

Can you please advise on the optimal upgrade procedure, and possibly 
give some general recommendations and warnings about possible issues?

According to the Samba Wiki at 
  https://wiki.samba.org/index.php/Upgrading_a_Samba_AD_DC
, it seems that this procedure might work:

- on FSMO DC, backup domain (samba-tool domain backup online ...)

- demote non-FSMO DC (samba-tool domain demote ...), shutdown VM

- run new VM with actual Samba-4.22.x DC installed, with same hostname,
  realm,... as had previously removed machine.

- join to domain (samba-tool domain join ...)

- start Samba and run AD replication status and Samba AD DC database 
 check (samba-tool drs showrepl ... / samba-tool dbcheck ...)

- transfer FSMO role to newly joined DC (samba-tool fsmo transfer...)
 (is it really needed? What about seizing a FSMO Role at the whole end?
 - but Wiki say FSMO transfer is recommeded before seizing)

- demote former FSMO, stop Samba and shutdown this old VM

- run another new VM with actual Samba-4.22.x DC prepared, with same 
  hostname, realm,... as had previously removed former FSMO.

- join it to AD, start Samba, check replication and DB status, maybe 
  transfer FSMO here again..(or seize FSMO here?)
 
- upgrade AD schema version (samba-tool domain schemaupgrade...) to
  value 88 


Apart from the fact that I am not sure that the above procedure is correct 
and optimal, there are still some ambiguities, e.g.:

- already mentioned above - can there be no server FSMO role defined 
anywhere (during the upgrade)? (and then seizing if at final end)

- Since Samba-4.9.5 supports a higher (but experimental) schema 69 
(Server 2012R2), wouldn't it be better to upgrade the AD schema to this 
level on the old DCs (and at end only do a schema upgrade 69 -> 88)?
-- 
I apologize for the possibly too amateurish questions, bad English, etc.
Franta Hanzlík