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Feature Descriptions for Linux and FreeBSD virtual machines on Hyper-V

Joshua R. Poulson|Last Updated: 1/9/2017
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6 Contributors

Applies To: Windows Server 2016, Hyper-V Server 2016, Windows Server 2012 R2, Hyper-V Server 2012 R2, Windows Server 2012, Hyper-V Server 2012, Windows Server 2008 R2, Windows 10, Windows 8.1, Windows 8, Windows 7.1, Windows 7

This article describes features available in components such as core, networking, storage, and memory when using Linux and FreeBSD on a virtual machine.

Core

FeatureDescription
Integrated shutdownWith this feature, an administrator can shut down virtual machines from the Hyper-V Manager. For more information, see Operating system shutdown.
Time synchronizationThis feature ensures that the maintained time inside a virtual machine is kept synchronized with the maintained time on the host. For more information, see Time synchronization.
Windows Server 2016 Accurate TimeThis feature allows the guest to use the Windows Server 2016 Accurate Time capability, which improves time synchronization with the host to 1ms accuracy. For more information, see Windows Server 2016 Accurate Time
Multiprocessing supportWith this feature, a virtual machine can use multiple processors on the host by configuring multiple virtual CPUs.
HeartbeatWith this feature, the host to can track the state of the virtual machine. For more information, see Heartbeat.
Integrated mouse supportWith this feature, you can use a mouse on a virtual machine's desktop and also use the mouse seamlessly between the Windows Server desktop and the Hyper-V console for the virtual machine.
Hyper-V specific Storage deviceThis feature grants high-performance access to storage devices that are attached to a virtual machine.
Hyper-V specific Network deviceThis feature grants high-performance access to network adapters that are attached to a virtual machine.

Networking

FeatureDescription
Jumbo framesWith this feature, an administrator can increase the size of network frames beyond 1500 bytes, which leads to a significant increase in network performance.
VLAN tagging and trunkingThis feature allows you to configure virtual LAN (VLAN) traffic for virtual machines.
Live MigrationWith this feature, you can migrate a virtual machine from one host to another host. For more information, see Virtual Machine Live Migration Overview.
Static IP InjectionWith this feature, you can replicate the static IP address of a virtual machine after it has been failed over to its replica on a different host. Such IP replication ensures that network workloads continue to work seamlessly after a failover event.
vRSS (Virtual Receive Side Scaling)Spreads the load from a virtual network adapter across multiple virtual processors in a virtual machine.For more information, see Virtual Receive-side Scaling in Windows Server 2012 R2.
TCP Segmentation and Checksum OffloadsTransfers segmentation and checksum work from the guest CPU to the host virtual switch or network adapter during network data transfers.
Large Receive Offload (LRO)Increases inbound throughput of high-bandwidth connections by aggregating multiple packets into a larger buffer, decreasing CPU overhead.
SR-IOVSingle Root I/O devices use DDA to allow guests access to portions of specific NIC cards allowing for reduced latency and increased throughput. SR-IOV requires up to date physical function (PF) drivers on the host and virtual function (VF) drivers on the guest.

Storage

FeatureDescription
VHDX resizeWith this feature, an administrator can resize a fixed-size .vhdx file that is attached to a virtual machine. For more information, see Online Virtual Hard Disk Resizing Overview.
Virtual Fibre ChannelWith this feature, virtual machines can recognize a fiber channel device and mount it natively. For more information, see Hyper-V Virtual Fibre Channel Overview.
Live virtual machine backupThis feature facilitates zero down time backup of live virtual machines.

Note that the backup operation does not succeed if the virtual machine has virtual hard disks (VHDs) that are hosted on remote storage such as a Server Message Block (SMB) share or an iSCSI volume. Additionally, ensure that the backup target does not reside on the same volume as the volume that you back up.
TRIM supportTRIM hints notify the drive that certain sectors that were previously allocated are no longer required by the app and can be purged. This process is typically used when an app makes large space allocations via a file and then self-manages the allocations to the file, for example, to virtual hard disk files.
SCSI WWNThe storvsc driver extracts World Wide Name (WWN) information from the port and node of devices attached to the virtual machine and creates the appropriate sysfs files.

Memory

FeatureDescription
PAE Kernel SupportPhysical Address Extension (PAE) technology allows a 32-bit kernel to access a physical address space that is larger than 4GB. Older Linux distributions such as RHEL 5.x used to ship a separate kernel that was PAE enabled. Newer distributions such as RHEL 6.x have pre-built PAE support.
Configuration of MMIO gapWith this feature, appliance manufacturers can configure the location of the Memory Mapped I/O (MMIO) gap. The MMIO gap is typically used to divide the available physical memory between an appliance's Just Enough Operating Systems (JeOS) and the actual software infrastructure that powers the appliance.
Dynamic Memory - Hot-AddThe host can dynamically increase or decrease the amount of memory available to a virtual machine while it is in operation. Before provisioning, the Administrator enables Dynamic Memory in the Virtual Machine Settings panel and specify the Startup Memory, Minimum Memory, and Maximum Memory for the virtual machine. When the virtual machine is in operation Dynamic Memory cannot be disabled and only the Minimum and Maximum settings can be changed. (It is a best practice to specify these memory sizes as multiples of 128MB.)

When the virtual machine is first started available memory is equal to the Startup Memory. As Memory Demand increases due to application workloads Hyper-V may dynamically allocate more memory to the virtual machine via the Hot-Add mechanism, if supported by that version of the kernel. The maximum amount of memory allocated is capped by the value of the Maximum Memory parameter.

The Memory tab of Hyper-V manager will display the amount of memory assigned to the virtual machine, but memory statistics within the virtual machine will show the highest amount of memory allocated.

For more information, see Hyper-V Dynamic Memory Overview.

Dynamic Memory - BallooningThe host can dynamically increase or decrease the amount of memory available to a virtual machine while it is in operation. Before provisioning, the Administrator enables Dynamic Memory in the Virtual Machine Settings panel and specify the Startup Memory, Minimum Memory, and Maximum Memory for the virtual machine. When the virtual machine is in operation Dynamic Memory cannot be disabled and only the Minimum and Maximum settings can be changed. (It is a best practice to specify these memory sizes as multiples of 128MB.)

When the virtual machine is first started available memory is equal to the Startup Memory. As Memory Demand increases due to application workloads Hyper-V may dynamically allocate more memory to the virtual machine via the Hot-Add mechanism (above). As Memory Demand decreases Hyper-V may automatically deprovision memory from the virtual machine via the Balloon mechanism. Hyper-V will not deprovision memory below the Minimum Memory parameter.

The Memory tab of Hyper-V manager will display the amount of memory assigned to the virtual machine, but memory statistics within the virtual machine will show the highest amount of memory allocated.

For more information, see Hyper-V Dynamic Memory Overview.

Runtime Memory ResizeAn administrator can set the amount of memory available to a virtual machine while it is in operation, either increasing memory ("Hot Add") or decreasing it ("Hot Remove"). Memory is returned to Hyper-V via the balloon driver (see "Dynamic Memory - Ballooning"). The balloon driver maintains a minimum amount of free memory after ballooning, called the "floor", so assigned memory cannot be reduced below the current demand plus this floor amount. The Memory tab of Hyper-V manager will display the amount of memory assigned to the virtual machine, but memory statistics within the virtual machine will show the highest amount of memory allocated. (It is a best practice to specify memory values as multiples of 128MB.)

Video

FeatureDescription
Hyper-V-specific video deviceThis feature provides high-performance graphics and superior resolution for virtual machines. This device does not provide Enhanced Session Mode or RemoteFX capabilities.

Miscellaneous

FeatureDescription
KVP (Key-Value pair) exchangeThis feature provides a key/value pair (KVP) exchange service for virtual machines. Typically administrators use the KVP mechanism to perform read and write custom data operations on a virtual machine. For more information, see Data Exchange: Using key-value pairs to share information between the host and guest on Hyper-V.
Non-Maskable InterruptWith this feature, an administrator can issue Non-Maskable Interrupts (NMI) to a virtual machine. NMIs are useful in obtaining crash dumps of operating systems that have become unresponsive due to application bugs. These crash dumps can be diagnosed after you restart.
File copy from host to guestThis feature allows files to be copied from the host physical computer to the guest virtual machines without using the network adaptor. For more information, see Guest services.
lsvmbus commandThis command gets information about devices on the Hyper-V virtual machine bus (VMBus) similiar to information commands like lspci.
Hyper-V SocketsThis is an additional communication channel between the host and guest operating system. To load and use the Hyper-V Sockets kernel module, see Make your own integration services.
PCI Passthrough/DDAWith Windows Server 2016 administrators can pass through PCI Express devices via the Discrete Device Assignment mechanism. Common devices are network cards, graphics cards, and special storage devices. The virtual machine will require the appropriate driver to use the exposed hardware. The hardware must be assigned to the virtual machine for it to be used.

For more information, see Discrete Device Assignment - Description and Background.

DDA is a pre-requisite for SR-IOV networking. Virtual ports will need to be assigned to the virtual machine and the virtual machine must use the correct Virtual Function (VF) drivers for device multiplexing.

Generation 2 virtual machines

FeatureDescription
Boot using UEFIThis feature allows virtual machines to boot using Unified Extensible Firmware Interface (UEFI).

For more information, see Generation 2 Virtual Machine Overview.
Secure bootThis feature allows virtual machines to use UEFI based secure boot mode. When a virtual machine is booted in secure mode, various operating system components are verified using signatures present in the UEFI data store.

For more information, see Secure Boot.

See Also

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