Upgrade Domain Controller /w a Child domain

Question

Hello

First I want to tell you I have preformed many upgrades from 2003 to 2019. All those steps in between, I know. But never when there is a child domain.

I have four DC's, 2008R2. two of these are for the parent XYZ.com and two are the child ABC.XYZ.com. When upgrading to 2019, I create 2012R2 server as a stepping stone. Should I upgrade the child domain first to 2019 servers, then the Parent? And do I need two 2012R2 servers, one to migrate the child and 1 to migrate the Parent?

Thanks in advance!

RSC

Answer 1

There should be no need in a two step. Though it shouldn't matter I'd probably do the child domain as first step.

The two prerequisites to introducing the first 2019 domain controller are that domain functional level needs to be 2008 or higher and older sysvol FRS replication needs to have been migrated to DFSR
https://techcommunity.microsoft.com/t5/Storage-at-Microsoft/Streamlined-Migration-of-FRS-to-DFSR-SYSVOL/ba-p/425405

I'd use dcdiag / repadmin tools to verify health correcting all errors found before starting any operations. Then stand up the new 2019, patch it fully, license it, join existing domain, add active directory domain services, promote it also making it a GC (recommended), transfer FSMO roles over (optional), transfer pdc emulator role (optional), use dcdiag / repadmin tools to again verify health, when all is good you can decommission / demote old one.

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