Windows Server 2012 (Hyper-V) Core Installation

The Performance Tuning Guidelines for Windows Server 2012 document is available and I’m reviewing and commenting on notable text in it.

On the subject of a Core installation of Windows Server 2012, the document says:

It features a smaller disk, memory profile, and attack surface. Therefore, we highly recommend that Hyper-V virtualization servers use the Server Core installation option. Using Server Core in the root partition leaves additional memory for the virtual machines to use (approximately 80 MB for the commit charge on a 64-bit edition of the Windows Server operating system).

You’ll save a couple of GB on disk space. When I’m able to buy disks smaller than 300 GB for my hosts I’ll care about this. Smaller disks are price listed, but my experience is that you’ll wait 3 months for them.

I don’t care about saving 80 MB of RAM on hosts with 48 GB, 192 GB, 256 GB, or 4 TB of RAM.

The other pro-Core argument is the number of security patches. I don’t care if I have 1 or 12 patches to install per month. I care about how many reboots I have to do; 1 patch = 1 reboot, 20 patches = 1 reboot. And on reboots, Cluster Aware Updating orchestrates that so I have no service downtime.

I care about easy administration. When there is a problem, I don’t want to be googling PowerShell. I sure as hell don’t want a junior operator/engineer to be searching the net for PowerShell alternatives to tasks that are quick/easy in the GUI. And until the h/w vendors have given us easy/complete non-GUI options for hardware management/troubleshooting, the Full installation is my recommendation, despite what Redmond says.

Microsoft’s recommendation remains unchanged from W2008 and W2008 R2. The Great Big Hyper-V Survey of 2011 shows only a very small percentage of you agreed to follow Microsoft’s advice on Core in the past.  One thing has changed in WS2012.

You can switch on the GUI in a Core via Server Manager, but it requires a reboot, and booting any new piece of server hardware takes 10 minutes these days (compare a WS2012 boot on a PC or laptop where it’s seconds).  That’s 10 minutes more for the customer or boss to be in your ear asking when their email will be back up and running.

In my opinion and experience, the cost of the full GUI is negligible and therefore I continue to recommend that type of installation.  I will consider changing my mind when I can flip from Core-GUI-Core without a reboot.

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10 Replies to “Windows Server 2012 (Hyper-V) Core Installation”

  1. One thing about patching: The number of critical restart-needing pathces are way lower on Core edition than on regular GUI-based. On a comparison based on Windows 2008R2, figuers showed that on core edition, mean time between restart-needing critical patches for the Windows OS was somewhere around 11 months. On the full OS, much lower. Might be a point to consider.

    Here’s some info from the team on the subject:

    • Trond,
      On a WS2012 cluster I really couldn’t give a hoot about reboots. With cluster aware updating, I have automated orchestration of VM workloads, host patching during the day while I’m around, and zero service downtime. Full install for me 🙂

  2. the only reason why I would ever do it is if they really need less reboot / patches.

    Taken from Virtual PC guy blog :

    Interestingly enough, just prior to going to TechED US there were some updates provided for the Windows Server 2012 Release Candidate. All of my systems that were running Server Core or a Minimal Server installation only received one update – and did not need to reboot. But my installations of Windows Server with a GUI received two updates, and needed to reboot afterwards.

  3. If OS install gets under 4GB with core, then it would be worth it to me, because I’ve been running ESXi on a 4GB SD (not SSD) card, and it would be nice to have to install an additional HD to make the switch. Any idea what size HD core requires?

    • Think it’s 6-8GB. I know Dell don’t support that type of boot for W2008 R2 (I asked a very senior person). They’ve had a kit to support it from MSFT ofr years AFAIK, but have ignored it. Never seen the option from MSFT. Hard to get small devices like that any more (camera business drives SD/CF card business) so 32 GB cards will be the norm soon enough and plenty enough for a full install 🙂

  4. Here’s my arguments (opinion) on why I recommend server core.

    On a single host using DAS storage, it would be important to reduce the amount of reboots required, which makes server core more sensible.

    For a cluster scenario, imagine a 2 host system, while Host A reboots for windows updates, what happens if Host B fails? During the reboot, you are at risk of everything being unavailable. So less frequent reboots with core would reduce the risk of complete cluster down time.

    Server core reduces the attack surface. There are less vulnerabilities for your system to be attacked. For example, your junior admin is on the host, then while searching online for an error you received, they click on a malicious 0 day site? I would feel the need now to run antivirus/antimalware to help protect from this possibility, but do I really want to risk that possibility on a host that is running a bunch of VM’s?

    Thinking of Antivirus/Antimalware, if I reduce my attack surface, then maybe I don’t need antivirus/antimalware on the host (I know, I’m treading on a big debate with this one).

    Now what about the system admins. With full GUI being available, it is a lot “easier” to install unnecessary tools on the HyperV host. What if an app they loaded causes stability issues?

    While the Core edition maybe a smaller footprint, I actually look at it based on the risk factors. I want to reduce my risks to keep my uptime higher.

    That being said, is this risk reduction worth the difficulty of troubleshooting and fixing a system. If I need to spend a lot time searching for powershell commands, and the system is down during that time, was it worth the risk reduction?

    Just my thoughts and opinion, I do believe you make a good case about the troubleshooting/repair time, and is a serious question that needs to be considered. Especially with the lack of good hardware (and software) provider support for server core!

  5. And what about Minimal Install? As Ben Armstrong is quoted above, servers with Core and Minimal receive less updates that require restart, while Minimal provides you with the ability to manage with a gui while keeping the attach surface smaller than Full. I am thinking of switching from Full to Minimal when we upgrade to WS2012.

    • My problem with Minimal is that some critical hardware troubleshooting tools require IE and Minimal GUI doesn’t include IE.

  6. Very nicely put!
    One thing about ESXi from VMware is there is enough of a text menu interface to do a few simple tasks but you always need a management PC.

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