Warning on Windows Server 2016 Deduplication Corruption

UPDATE 2 – 2017/02/06

DO NOT INSTALL KB3216755 if you don’t need it.  Huge memory leak reported to associated with this. If you need it I’d consider all my options.

UPDATE – GET KB3216755

As you can read it the comments, Microsoft reached out and confirms the issues are fixed as part of KB3216755 => https://support.microsoft.com/en-us/help/4011347/windows-10-update-kb3216755 . I commend them for responding so quickly and getting it sorted. Do not that at the time of writing this (late on January 30th CET) the Windows Sever 2016 update isn’t in the Windows Catalog yet, only the Windows 10 ones. But Microsoft confirms you should install the update  on their blog

Windows Server 2016 Data Deduplication users: please install KB3216755!

The issue

Good morning. A quick blog post to give a heads up to my readers who might not be subscribed to Anton Gostev (Veeam) his “The Word Form Gostev”. It concerns a warning on Windows Server 2016 Deduplication corruption.

Warning on Windows Server 2016 Deduplication Corruption

There are multiple reports of data corruption with Windows Server 2016 deduplication. One is related to file sizes over 2TB. The other with the loss of checksum values. Microsoft is aware these issues and a fix is coming for these issues.

I quote Gostev

I’ve already received the official confirmation from Microsoft that this is the know issue (ID 10165851) which is scheduled to be addressed in the next Windows Server 2016 servicing update. There are actually two separate issues, both leading to file corruption when using deduplication on very large files. One issue occurs when files grow to 2.2TB or larger, and another one causes loss of checksums for files with “smaller sizes” – this is the actual wording of the official note, so I have no idea how small

What to do?

If you use Windows Server 2016 deduplication for backups, create new full backups regularly. Also make sure you do backup integrity testing and restore tests. Follow up on the update when it arrives.

If you use the for production data make sure you have frequent and validated backups! Design & operate under the mantra of “Trust but verify”.

Also, we’ve heard reports and noticed that Windows Server 2016 Deduplication resource configuration isn’t always respected. I.e. it can take all resources away despite limitations being set. We hope a fix for this is also under way.

Migrate a Windows Server 2012 R2 AD FS farm to a Windows Server 2016 AD FS farm


I recently went through the effort to migrate a Windows Server 2012 R2 AD FS farm to a Windows Server 2016 AD FS farm. For this exercise the people in charge wanted to maintain the server names and IP addresses. By doing so there is no need for changes in the Kemp Technologies load balancer.

Farm Behavior Level Feature

In Windows Server 2016 ADFS we now have a thing called  the Farm Behavior Level (FBL)  feature (FBL). It  determines the features that the AD FS farm can use. Optimistically you can state that the FBL of a Windows Server 2012 R2 AD FS farm is at the Windows Server 2012 R2 FBL.

The FBL feature and mixed mode now makes a “trick” many used to upgrade a ADFS farm to AD FS Windows Server 2012 R2 organizations without the hassle of setting up a new farm and exporting / importing the configuration possible. looking to upgrade to Windows Server 2016 will not have to deploy an entirely new farm, export and import configuration data. Instead, they can add Windows Server 2016 nodes to an existing farm while it is online and only incur the relatively brief downtime involved in the FBL raise.

We can add a secondary Windows Server 2016 AD FS server to a Windows Server 2012 R2 farm. The farm will continue operating at the Windows Server 2012 R2 FBL. This is “mixed mode” so to speak. There is no need to move all the node to the same version immediately.

As long as you are in mixed mode you don’t get the benefits of the new capabilities and features in Windows Server 2016 ADFS. These are not available.

Administrators can add new, Windows Server 2016 federation servers to an existing Windows Server 2012 R2 farm. As a result, the farm is in “mixed mode” and operates the Windows Server 2012 R2 farm behavior level.

When all Windows Server 2012 R2 nodes have been removed form the farm and all nodes are Windows Server 2016 you can raise the FBL level. This results in the new Windows Server 2016 ADFS features being enabled and ready for configuration and use.

The Migration Path Notes


You cannot in place upgrade a Windows Server 2012 R2 ADFS Farm node to Windows Server 2016. You will need to remove it from the farm and replace it with a new Windows Server 2016 ADFS node.


In this migration we are preserving the node names and IP addresses. This means the load balancer needed no configuration changes. So in that respect this process is different from what is normally recommended.

This is a WID based deployment example. You can do the same for an SQL based deployment.

The FBL approach is only valid for a migration from Windows Server 2012 AD FS to Windows Server 2016 AD FS. A migration from AD FS 2.0 or 2.1 (Windows Server 2008 R2 or Windows Server 2012) requires the use of the Export-FederationConfiguration and Import FederationConfiguration as before.

Also see https://technet.microsoft.com/en-us/windows-server-docs/identity/ad-fs/overview/ad-fs-2016-requirements

Step by Step

  • Start with the secondary nodes. For each of them make sure you have the server name and the IP configuration.
  • Make sure you have the Service Communications SSL cert for your AD FS and the domain or managed service account name and password.
  • Make sure you have an ADFS configuration backup and also that you have a backup or an export (cool thing about VMs) of the VMs for rapid recovery if needed.

Remove the ADFS role via Server management


  • Shut down the VM
  • Edit the setting and remove the OS VHDX. Delete the file (you have a backup/export)
  • Copy your completely patched and syprepped OS VHDX with Windows Server to the location for this VM. Rename that VHDX to something sensible like adfs2disk01.vhdx.
  • Edit the settings and add the new sysprepped OS VHDX to the VM. Make sure that the disk is 1st in the boot order.
  • Start the VM
  • Go through the mini wizard and log in to it.
  • Configure the NIC with the same setting as your old DNS Server
  • Rename the VM to the original VM name and join the domain.
  • Restart the VM
  • Login to the VM and Install ADFS using Add Roles and Features in Server Manager


  • When done configure ADFS


  • Select to add the node to an existing federation farm


  • Make sure you have an account with AD admin permissions


  • Tell the node what primary federation server is


  • Import your certificate


  • Specify the ADFS Service account and its password


  • You’re ready to go on


  • If any prerequisites don’t work out you’ll be notified, we’re good to go!


  • Let the wizard complete all it steps


  • When the configuration is done you need to restart the VM to complete adding the node to the ADFS farm.


  • Restart your VM and log back in. When you open up ADFS  you’ll see that this new Windows Server 2016 node is a secondary node in your ADFS Farm.


  • Note that from a load balancer perspective nothing has changed. They just saw the node go up and down a few times; if they were paying attention at all that is.
  • Now repeat the entire process for all you secondary ADFS Farm nodes. When done we’ll swap the primary node to one of the secondary nodes. This is needed so you can repeat the process for the last remaining node in the farm, which at that time needs to be a secondary node. In the example of our 2 node farm we swap the roles between ADFS1 and ADFS2.


  • Verify that ADFS2 is the primary node and if so, repeat the migration process for the last remaining node (ADFS1) in our case.
  • Once that’s been completed we swap them back to have exactly the same situation as before the migration.


  • On the primary node run Get-AdfsFarmInformation (a new cmdlet in Windows Server 2016 R2).


  • You’ll see that our current farm behavior is 1 and our 2 nodes (all of them Windows Server 2016) are listed. Note that any nodes still on Windows Server 2012 R2 would not be shown.

WARNING: to raise the FBL to Windows Server 2016 your AD Schema needs to be upgraded to at least Windows Server 2016 version 85 or higher. This is also the case form new AD FS farm installations which will be at the latest FBL by default. My environment is already 100% on Windows Server 2016 AD. So I’m good to go. If yours is not, don’t forget to upgrade you schema. You don’t need to upgrade your DC’s unless you want to leverage Microsoft Password authentication, then you need al least 1 Windows Server 2016 domain controller. See https://technet.microsoft.com/en-us/windows-server-docs/identity/ad-fs/overview/ad-fs-2016-requirements

  • As we know all our nodes are on Windows Server 2016 we can raise our Farm Behavior Level  (FBL) by running Invoke-AdfsFarmBehaviorLevelRaise


  • Just let it run it has some work to do including creating a new database.


  • It will tell you when it’s done and point out changes in the configuration.


  • Now run Get-AdfsFarmInformation again


  • Note that the  current farm behavior is 3 and our 2 nodes (all of them Windows Server 2016) are listed. Note that  if any nodes had still been on Windows Server 2012 R2 they would have been kicked from the farm and should be removed form the load balancer.


PS: with some creativity and by having a look at my blog on https://blog.workinghardinit.work/2016/11/28/easily-migrating-non-ad-integrated-dns-servers-while-preserving-server-names-and-ip-addresses/ You can easily figure out how to add some extra steps to move to generation 2 VMs while you’re at it if you don’t use these yet.

Changes in RDP over UDP behavior in Windows 10 and Windows 2016


With Windows Server 2012 and Windows 8 (and Windows 7 RDP client 8.0) with some updates we got support for RDP to use UDP for data transport. This gave us a great experience over less reliable to even rather bad networks.

Anecdote: I was in an area of the world where there was no internet access available bar a very bad and lousy Wi-Fi connection at the shop/cafeteria. That was just fine, I wasn’t there for the great Wi-Fi access at all. But I needed to check e-mail and that wasn’t succeeding in any way, the network reliability was just too bad. I got the job done by using RDP to connect to a workstation back home (across the ocean on another continent) and check my e-mail there. Not a super great experience but UDP made it possible where nothing else worked. I was impressed.

Changes in RDP over UDP behavior in Windows 10 and Windows 2016

When connecting to Windows Server 2016 or a Windows 10 over a RD Gateway we see 1 HTTP and only one UDP connection being established for a session. We used to see 1 HTTP and 2 UDP connections per session with Windows 8/8.1 and Windows Server 2012(R2)

It doesn’t matter if your client is running RDP 8.0 or RDP 10.0 or whether the RD Gateway itself is running Windows Server 2012 R2 or Windows Server 2016. The only thing that does matter is the target that you are connecting to.

Also, this has nothing to do with a Firewall or so acting up, we’re testing with and without with the same IP etc. Let’s take a quick look at some examples and compare.

When connecting to Windows 10 or Windows Server 2016 we see that 1 UDP connection is established.

In total, there are 8 events logged for a successful connection over the RDG Gateway.


You’ll find 2 event ID 302 events (1 for a HTTP connection and 1 for a UDP connection) as well as 1 Event ID 205 events for the UDP proxy usage.



In the RD Gateway manager, monitoring we can see 1 HTTP and the 1 UDP connections for one RDP Session to a Windows 2016 Server.


When connecting to Windows 8/8.1 or Windows Server 2012 (R2) we see that 2 UDP connections are established.

In total, there are 10 events logged for a successful connection over the RDG Gateway:


You’ll find 3 event ID 302 events (1 for a HTTP connection and 2 for a UDP connection) as well as 2 Event ID 205 events for the UDP proxy usage.

In the RD Gateway manager, monitoring we can see 1 HTTP and the 2 UDP connections for one RDP Session to a Windows 2012 R2 Server.


So, RDP wise something seems to have changed. But I do not know the story and why.

Kick start ADFS when your self- signed certificates have expired already

I recently had to do some lab work on a Windows Server 2012 R2 ADFS farm to prep for a migration to Windows Server 2016.  Due to some storage shortage and some upgrades and migrations (all hardware in the lab runs Windows Server 2016) I had parked my Windows Server 2012 R2 ADFS farm offline.

So when I copied them back to my cluster and imported them I knew I had to make sure the domain was OK. This is easy enough, just run:

Reset-ComputerMachinePassword [-Credential Mydomain\bigadmin -Server MyDC01

That worked like a charm and soon enough my 2 VMs where up an running happily in the domain. I did have some issues however. My AFDS servers had been of line long enough before the expiration of the token-decrypting and the token-signing certificates to not yet have generate the new certificates for auto renewal and long enough to have them expire already. Darn!


The result was a bunch of errors in the event log as you might expect and appreciate.


An error occurred during an attempt to build the certificate chain for configuration certificate identified by thumbprint ’26AFDC4A226D2605955BF6F844F0866C14B1E82B’. Possible causes are that the certificate has been revoked or certificate is not within its validity period.
The following errors occurred while building the certificate chain: 
MSIS2013: A required certificate is not within its validity period when verifying against the current system clock.

But this also raised the question on how to get the ADFS servers back in a working condition. Normally these are generated automatically close to the expiration date of your existing certs (or at the critical threshold you configured). So I disabled / re-enabled auto certificate rollover but does actually does it even kick in if you have already expired? That I don’t know and I really had no time to wait hours or days to see what happens.

Luckily there is a command you can issue to renew the certificates immediately. This is the same command you can use when you have disabled auto rollover and need it re-enabled. That works normally after some patience.

Update-AdfsCertificate -Urgent

The result was immediate, the self signing certs were renewed.


And we can see this in the various entries in the event log


Do note that this command will cause a disruption of the service with your partners until they have refreshed the information from your federation metadata – or in the case this isn’t or can’t be leveraged, manually updated. In my case I had a “service down” situation anyway, but in normal conditions you’d plan this and follow the normal procedure you have in place with any partner that need your ADFS Services.