I really, really hope these haven't been in-place upgrades. That is, you installed a new server, joined it to the domain, DC-promoed it, transferred the FSMOs, then unpromoted the legacy DC before removing it from the domain. If you did do an in-place upgrade, you probably have a huge Windows.old folder in C: drive.
Assuming it was a clean build, 2019 has a lot of telemetry and monitoring tools turned on by default.
- Disable telemetry:
- Diagnostic data - Off.
- Tailored experiences – Off.
- Feedback frequency – Never.
Stop and disable UALSvc (User Access Logging Service) and clear out files and folders in \Windows\System32\Logfiles\SUM\
Run Get-WindowsErrorReporting to see if WER is enabled. If it is, run Disable-WindowsErrorReporting to disable it.
Clean up Winsxs. From an elevated command prompt, run cleanmgr.exe /verylowdisk. Or run CleanMgr interactively and select the option to scan and clean Windows system files (including updates). If Winsxs doesn't seem to be changing in size even after disk cleanup (and reboot), run SFC /scannow to ensure no system files are corrupt. 8 GB or so Winsxs folder size seems to be typical for an averagely-maintained server.
Check the Software Distribution folder. If it's many GB, run the following in an elevated command prompt to stop Windows Update services and BITS and clear it out.
net stop bits
net stop wuauserv
for /d %G in ("C:\Windows\SoftwareDistribution\*") do rd /s /q "%~G"
net start wuauserv
Uninstall any Windows features you aren't using on the server. Running Acronis on a DC seems unfortunate to me (running it on a separate server/workstation seems best). Once you've uninstalled Windows features, let it run a while and ensure no issues. If none, consider running Remove-Windowsfeature [featurename] -Remove on the features you already uninstalled. This will completely remove the binaries (and make patching faster). Note that you will need a Window Server 2019 install disk or ISO if you decide you need any of those features back in future.
If this still doesn't free up enough space, download Treesize Free and run it to discover what's consuming C drive. By default, it will sort by the largest folder sizes. Winsxs and System32 are likely to be the largest (much of System32 is actually symlinks to files in Winsxs). For anything else on C: that seems to be consuming many GB, if necessary, google the folder to see what it is and the safe method to delete the files (if it's something obvious like IIS log files, then delete what you don't need). Run Treesize multiple times over a few days to see what might be growing.
