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Windows Server is a crucial part of the software stack, but the full OS can be overkill for certain enterprise workloads.
Microsoft removed the GUI in the Nano Server and Server Core installation options of Windows Server 2016 to cut the number of running services and processes. Because the smaller OS requires fewer resources, this frees more of the server's RAM and compute power to operate more demanding workloads or additional VMs.
Microsoft estimates the virtual hard disk size for a full Windows Server 2016 installation at just over 10 GB, while a Server Core installation takes up slightly more than 6 GB of disk space. The minimal deployment footprint reduces the attack surface, which cuts down the time IT departments spend installing security updates.
Microsoft intends to remove the infrastructure role capabilities from Nano Server in the September 2017 semiannual channel update to further optimize that OS for container use. This leaves Server Core as administrators' sole minimal-footprint option for general-purpose server deployments. Here are the system requirements, roles and challenges associated with a Server Core installation.
Typical Server Core uses
Microsoft recommends the following roles for a Server Core installation:
- Active Directory (AD) Certificate Services;
- AD Domain Services;
- AD Lightweight Directory Services;
- AD Rights Management Services;
- Dynamic Host Configuration Protocol Server;
- Domain Name System Server;
- File Services;
- Licensing Server;
- Print and Document Services;
- Remote Desktop Services Connection Broker;
- Routing and Remote Access Server;
- Streaming Media Services;
- Web Server (including a subset of ASP.NET);
- Windows Server Update Server; and
- Volume Activation Services.
For workloads that do not require a GUI, use a lab to test the installation and functionality of Server Core, the workload and the associated management tools before a move to the live environment.
System requirements for a Server Core installation
While administrators can follow Microsoft's minimum requirements for a Windows Server 2016 installation, that leaves few host resources available to properly run a workload -- or multiple workloads in VMs.
Microsoft refrains from system requirement recommendations because not all server roles need the same amount of resources. Administrators should run a test deployment to measure if the workload runs properly under a certain configuration and adjust if necessary.
The minimum system requirements listed below are the same to install Server Core, Server with Desktop Experience -- the full GUI version -- and Nano Server for both Standard and Datacenter editions of Windows Server 2016.
CPU: Windows Server 2016 needs a 1.4 GHz 64-bit processor with an x64 instruction set. The processor must support additional feature sets, including:
- No-eXecute on Advanced Micro Devices processors and eXecute Disable on Intel CPUs, which stop code execution in certain memory areas;
- data execution prevention, which runs additional memory checks to prevent malicious code; and
- second-level address translation support, which virtualizes memory space to reduce hypervisor overhead.
In addition, the processor must support:
- the CMPXCHG16B instruction for high-performance data operations;
- Load AH from Flags and Store AH to Flags commands, which load and store instructions for virtualization and floating-point conditions; and
- the PrefetchW instruction, which carries data closer to the CPU before a write.
Those are just the single-core clock and compatibility requirements. The number of processor cores -- and the cache size in each core -- affects overall performance. A processor with several cores and a larger cache supports more VMs.
Memory: Windows Server 2016 requires a minimum of 512 MB with error-correcting code or a similar technology. To create a VM, designate at least 800 MB or the setup will fail; after it's installed, lower the RAM allocation as needed.
Network adapter: Network adapters must support a minimum of 1 Gigabit Ethernet bandwidth and the preboot execution environment feature. The network adapter has to conform to the Peripheral Component Interconnect (PCI) Express design. Organizations that will run multiple VMs on a server can install more than one network adapter on the host to avoid a single point of failure.
Storage and storage controllers: Windows Server 2016 requires at least 32 GB of disk storage but will need more space if the installation occurs over a network.
Plot out additional storage for dump files, paging and hibernation. However, snapshot and replication features need more disk space when a VM uses Windows Server 2016 as the guest OS.
The server storage adapter must use the PCI Express architecture. Windows Server 2016 does not support the following storage interfaces for its data, boot or page drives: Advanced Technology Attachment, Parallel ATA, Integrated Drive Electronics and Enhanced IDE.
Trusted Platform: A Trusted Platform Module (TPM) chip is not necessary to install the OS, but security features, such as BitLocker Drive Encryption, require TPM version 2.0 or later. Systems that meet TPM 2.0 need SHA-256 platform configuration register banks.
Deploy and manage Server Core
The setup wizard performs a clean installation of the Windows Server 2016 OS. A dialog box offers the choice to use the full version of Windows Server with the GUI or Server Core.
Because Server Core lacks a GUI, administrators cannot monitor or manage those deployments with the graphical management tools, such as Server Manager, familiar to most Windows shops. Instead, they control Server Core through a command prompt with PowerShell or with Remote Server Administration Tools (RSAT).
PowerShell cmdlets let administrators install, uninstall and configure Server Core. Automate complex Server Core configuration tasks with PowerShell scripts, rather than clicking through a GUI to accomplish the task.
RSAT includes a mix of tools, such as Microsoft Management Console snap-ins, Windows PowerShell cmdlet modules and command-line utilities, to oversee Server Core roles and features. RSAT does not run on Windows Server; it only operates on supported client systems.
Potential trouble spots with Server Core
While Server Core is a fully functioning version of Windows Server 2016, there are several differences that could pose management difficulties for admins unfamiliar with the compact OS.
Users cannot convert a Server Core installation to a Server with Desktop Experience version. That conversion was possible with some earlier versions of Windows Server, but organizations that build a Server Core workload and then decide to switch to the full Windows Server 2016 option need to perform a clean installation. This reinstallation and reconfiguration process can cause downtime.
There are also risks and potential troubleshooting issues with Server Core management via the command line. Even the most skilled IT professionals type in the wrong PowerShell command and cause errors from time to time. Despite Server Core's advantages, many organizations prefer the familiar GUI administrative tools in the full Windows Server installation.
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