AADS and Virtualization




AADS Terminal Server and Virtualization

In case AADS is used within a VM, convert the AADS License to an Online License type. This needs to be done only once.

Every time when the VM has changed, for example more/less memory or different cpu,
or when the VM is moved to some other Server and the VM is now running on this other Server,
you need to do 3 steps:


Q: Does AADS Terminal Server work in a Virtualization Environment?

A: We think that is not the "correct" question. The question should be "does Virtualization work OK?". Also, we think that you should not ask us, but the VM vendor. If Virtualization would do a perfect job, the software running inside the VM would never know it is running inside a VM.

So, if a piece of software has problems when running inside a VM, but works OK when running on real hardware, you should contact the vendor of the VM and ask them to do a better Virtualization job. Apparently the VM is not close enough to the "real thing".

Q: OK, I understand; Virtualization does not work flawless. However, I still want to know about AADS Terminal Server and Virtualization. Does it work?

A: We use VMs ourselves. One of our favorites is VirtualBox . AADS Terminal Server runs OK in VirtualBox. Also you should check out the ChangeLog of VirtualBox. It gives you an idea of the number of issues related to Virtualization, assuming that other vendors work as hard as Sun/Oracle does on VirtualBox.

Q: What are the known problems of AADS Terminal Server and Virtualization?

A: We think that the question should be: What are the known problems of Virtualization. The known problems of Virtualization are mostly performance and network related.

About performance: Virtualization is slow. It can be very slow. We are aware of all the claims and all the stories you can read on the internet and from VM vendors about performance, but when we use it, it is significant slower then real hardware. It can be up till a factor 4 slower.

Q: Please tell me how you substantiate this statement about Virtualization being slow.

A: This is one of the tests we do


So, a server is used to run native Windows + AADS Terminal Server, OR to run it with a Virtualization layer in between it.

The result is, on average, that without Virtualization up till 4 times more users can login. So 100 users in case of no Virtualization versus 25 till 50 users in case of Virtualization.

Possible some tuning should have been applied. Possible Virtualization can perform better. But the bottom line is always the same: Virtualization is an extra layer that slows down whatever is being run inside the VM, and which could run faster on real hardware.

Q: Do you advise customers not to use Virtualization?

A: Certainly not. When you buy some extra cpu power and memory, and a modern, fast SSD harddisk, quite possible you can afford this loss of power. And there are a lot of other good reasons why Virtualization is a good idea.

Virtualization Settings: be sure to give "enough" resources to Windows

When running Windows inside a VM, be sure to give "enough" resources to Windows:

Virtualization and network problems

About network problems: UDP traffic is occasionally handled poorly by Virtualization. And this can be a problem, because Windows does use UDP. So your default Windows functionality like accessing a domain, or a drive mapping, might perform slower or might give you errors when Windows is running inside a VM.

Virtualization and "The Clock"

The clock of Windows when it is running inside a VM, might be having a problem, because:


2 separate processes and algorithms that both attempt to synchronize the clock of Windows. This can be the cause of a lot of trouble:

Due to this, the clock inside the VM can make "large jumps" in the time, forwards and backwards. On average Windows attempts to synchronize the clock once every 4 hours, implying "jumps" in the date and time, forwards or backwards every 4 hours.

When using the SSL gateway, or using SSL / HTTPS in general, this can be a big problem, because in order to be able to verify the validity of SSL connections, a good, accurate PC clock is required. The clock needs to have the right date and time. And should not jump forward or backwards. SSL might fail if the clock is incorrect. Or worse: SSL might accept an old expired SSL certificate if the PC clock has a date/time in the past.

The problem with the clock does not end here: Virtualization products do offer the ability to reduce the amount of cpu-cycles as available to the VM, for example because the Host needs to allocate and divide all cpu-cycles among all running VMs. However, this can cause trouble, because sometimes the clock-ticks and the progress of the clock inside the VM, depends on the continuity of cpu-cycles. A reduce in cpu-cycles can imply that the clock inside the VM runs slower, or even faster, because the clock-synchronize algorithms do try somehow to compensate for the lack of cpu-cycles.
Windows itself might behave "strange" when the available cpu-cycles are not constant, because sometimes time-outs are calculated and watched based on cpu-cycles or clock ticks. And when the VM is running with a variable number of cpu-cycles, processes running inside the VM might go wrong while handling time-outs.

When there are problems with SSL, be sure to check for the correct clock settings both on the Host and the VM. And check the Windows Eventlog for events indicating "large jumps" in the time, forwards and backwards.

Advise: Be sure to have correct clock settings on both the Virtualization Host and the VM, and be sure that there are no multiple clock-synchronize-settings applied to the VM. Make a choice: the PC clock should be synchronized with only 1 setting / algorithm.

AADS License and Virtualization

Q: I like Virtualization because it is so easy to copy and clone software, and to run software multiple times in multiple VMs. Is this also possible with AADS Terminal Server inside a VM?

A: This is a problem. Our main license term, and business, is 1 server, 1 license. So for obvious reasons we do not think it is acceptable to copy and clone licensed software and to run it as many times you want. Our main license term has no exception: 1 server, 1 license. This does also apply for VMs. This license term does always apply.

Q: What will happen when a copy and clone Windows + AADS Terminal Server and attempt to run it?

A: An AADS Terminal Server license is bound to the hard- and software of the server onto which it is installed. Therefore an AADS Terminal Server license does not work when AADS Terminal Server is running on some other hard- and/or software.

Q: Does this imply that I do not have the freedom to move a VM with Windows + AADS Terminal Server across all my Virtualization Servers?

A: Indeed: an AADS Terminal Server license will not work when you move a VM with Windows + AADS Terminal Server to another server.

However, an AADS Terminal Server license can be an Online License type. When an AADS Terminal Server license is an Online License type , you need to do 3 steps:

These 3 steps can be done in 1 minute.

Q: So I can move a VM with Windows + AADS Terminal Server across all my Virtualization Servers. How often can I do this?

A: We start with the following answer: The economic lifespan of a Server is 3 years. Not 3 months; not 3 days. So, the License Servers do start with the expectations that an AADS Terminal Server license is installed 1 time in 3 years.

It might happen that due to unforeseen reasons like failing servers, broken hard disk, etc, you have to install AADS Terminal Server more often. In case the next installation fails, you can always send an email to us, and we will assist you in fixing the issue.

Procedure and information about the Online License type

Click here for the procedure and information about the Online License type .

Copyright 2012-2018 AADS WorldWide LTD. AADS Terminal Server | Application Server | Remote Desktop solutions | Firewall