Active Directory Domain Controller Backups – Part 2

Time for part 2 of the “how to backup DCs” story. I’ll try to keep it more concise and just deliver the needed info.

In my previous post we established I was going for a backup to disk (another network share). I was also going to back up the system state of 2 DCs /domain, the list of GPOs and their links and the list of object DNs.

The process explained

I want to setup the backup in such a way, that it is more automated, and I don’t have to worry about checking all the bits and pieces are in place, and I also want to be able to update parts of the process without rebuilding everything. Therefore the process can be split in these parts:

1. Preparing accounts and permissions

2. Creating and delivering worker scripts (the scripts that actually do the job)

3. Setting up backup schedules (scheduled tasks run scripts from point 2, using credentials and resources setup at point 1)

Accounts and Permissions

You will need some accounts and groups setup so that you can safely transfer the backups from the DC to the backup share. The steps are outlined below:

  1. Create a Universal Security Group in one of your domains (top root domain, preferably) let’s call it “Global AD Backup Operators”. We will use this group below
  2. Create a network share on your choice for a backup backup location , where only “Domain Controllers” and “Global AD Backup Operators” have read/write access (Security and Sharing tabs). Refer to my previous post, for why this is important. You cannot use the “BUILTIN\Backup Operators” of the domain since that group is specific to DCs only.
  3. In the network share create a few subfolders, named DistinguishedNameBackup, GroupPolicyObjectBackup and WindowsImageBackup.
  4. Create an account in each domain that will run the backups. Make this account member of the “BUILTIN\Backup Operators” and the “Domain\Global AD Backup Operators” you created in Step 1. The Backup operators group is per domain, as you might know.
  5. Create a new GPO and link it to the “Domain Controllers” OU in each of your domains/ change your existing default Domain Controller Policy. In the policy you should include “BUILTIN\Backup Operators” in the list of accounts for “Allow logon as a batch job”.

Creating The Backup Scripts

Backing up the DC System State

If you don’t have the Windows Backup feature installed the snippet below will do that for you:

Import-Module ServerManager

if (!(Get-windowsFeature -Name Backup).Installed) { add-windowsfeature Backup}

Now for the backup itself you just run wbadmin wrapped up in some powershell code like below:


$WBadmin_cmd = "wbadmin.exe START BACKUP -backupTarget:$TargetUNC -allCritical -include:c: -noVerify -vssFull -quiet"
Invoke-expression $WBadmin_cmd

I used -allCritical instead of -SystemState, to include all that is necessary to do a bare metal recovery, other than that, nothing major to write home about. More info here.

Backing up Group Policy Objects and Links

Next step is to configure the backup of the GPO objects and the GP-Links. GP-links must be backed up separately since it is not stored in the GPO object, but in AD Database, on each object where the GPO is linked. This gets even more convoluted when you link GPO’s in different domains, than the domain they are created it. There are multiple ways to backup the GPOs:

-Using GPMC sample scripts, there is a script for backing up GPOs

-Using powershell module grouppolicy, running on windows 2008 R2 – I chose this one.

I also wanted to handle GPO backup history at script level, so, the script Backup-GPOs.ps1, attached to this post contains the “delete older than x days” logic to handle accumulating backups. The command to backup a GPO, looks like this:

backup-GPO -all  -domain $domain -path $path

The options are pretty self explanatory I suppose.The command to get all gpLink objects looks like this:

$gpl += get-adobject -filter '(objectCategory -eq "organizationalunit" -or distinguishedname -eq $domdn) -and gplink -like "[ldap://cn=*"' -searchbase $domdn -searchscope subtree -properties gplink,distinguishedname,gpoptions -server $env:ComputerNameps]</pre>
Now, I've read some of the people's experiences online and it seems that using the wildcard character for the backup GPO command has some inconsistent results, meaning, past a certain number of GPOs backed up, the cmdlet stops working properly. The solution would be to grab all GPOs and back them up in a <strong>for-each</strong> loop. This ties in pretty well with the fact that we need to map the GPO name with the gP-link information, so the core piece of the GPO backup script looks like this (most of the code is reused from <a href="">here</a>):

import-module grouppolicy
import-module activedirectory

#build a list of GPOs in current domains
$domobj = get-addomain
$dom = $domobj.dnsroot
$domdn = $domobj.distinguishedname
$gpocol += get-gpo -all -domain $dom

$gpl = $null

#build a list of gplink objects across the enterprise
$domains = get-adforest | select -ExpandProperty domains
$domains | % {
$domobj = get-addomain $_
$domdn = $domobj.distinguishedname
$gpl += get-adobject -filter '(objectCategory -eq "organizationalunit" -or distinguishedname -eq $domdn) -and gplink -like "[ldap://cn=*"' -searchbase $domdn -searchscope subtree -properties gplink,distinguishedname,gpoptions -server $domobj.PDCEmulator

#backup GPOs, map, GPOs to Target DNs
$section = "backup"
foreach ($gpo in $gpocol) {

$name = $gpo.displayname
new-item $curpath\$name -type directory -erroraction:silentlycontinue | out-null
$id = $
$configdn = (get-adrootdse).configurationNamingContext
backup-gpo -guid $id -domain $dom -path $curpath\$name | tee-object -variable msg
get-gporeport -guid $id -domain $dom -reporttype html -path $curpath\$name\$name.html
$gpl | % {if ($_.gplink -match $id) {$_.distinguishedname + "#" +  $_.gpoptions + "#" + $_.gplink} } | out-file -filepath $curpath\$name\gplinks-$id.txt -append


Just a little note here, the script is designed to get the gp-Links outside of the current domain of the account the script is running under. What differs from Frank Czepat’s script is the fact that i added a lookup to the $gpl variable and i pointed the get-adobject command to a specific DC (leaving it go for the default, would result in errors).

Backing up DistinguishedNames List

This is fairly easy and straightforward. While I could do this using powershell, i decided to go for the old and trusted dsquery, as it is faster than powershell code. Here we also have to deal with accumulating backups, as i built the script to output a timestamped file. The command that actually does the backup is this one:

$DomainDNsFile = "DomainDNs_$(get-date -Uformat "%Y%m%d-%H%M%S").txt"
$FilePath = "$curpath\$DomainDNsFile"
$DomainDNList_cmd = "dsquery * domainroot -scope subtree -attr modifytimestamp distinguishedname -limit 0 > $FilePath"
Invoke-expression $DomainDNList_cmd

I built these backup scripts as 3 individual files, you can download them from here Backup-Scripts.

That’s about it for how the backup is done, I guess more than half these items are sort of trivial to setup, the only tricky part is grabbing the gP-links, and creating a mapping between the GPO, and DNs in the gp-links

Next post in the series will discuss how to deliver and schedule these scripts on your domain controllers.

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