Reserves Tab: Reserves Tab allows you to set aside resources for the operating system on the destination Hyper-V host. Hyper-V host will not be available for placement or virtual machines will not be placed unless its resource requirements can be met without using host reserves. By default, when you add a Hyper-V host under VMM management, VMM configures Hyper-V host to inherit host reserve settings from the VMM Host group. “Override host reserves settings from the parent host group” option is unchecked as shown in the figure 1.0 below:
Figure 1.0: Host Reserves Tab for a Hyper-V Host
In case you wish to configure host reserves settings for individual Hyper-V host, check “Override host reserves settings from the parent host group” option and then configure the reserves settings as shown in the figure 1.1 below:
Figure 1.1: Configuring Host Reserve Settings for a Hyper-V Host
By default, host reserve settings are inherited from the VMM host group. However, you can always uncheck “Override host reserves settings from the parent host group” option to configure host reserve settings for individual Hyper-V host. Host reserve settings are very useful when you have a few virtual machines that need to be up and running on a particular virtualization host. Such virtual machines do not participate in live migration events and are always up and running on a particular virtualization host. Before the virtual machines can be placed on a virtualization host, the host must be able to meet the resource requirements of virtual machines without considering the host reserves. VMM always takes host reserve settings of virtualization hosts into consideration before the virtual machine can be moved to a virtualization host. As part of the host reserve setting, you can configure CPU, Memory, Disk Space, Disk I/O and Network I/O as shown in the screenshot above.
Host reserves setting can be configured for individual VMM host groups and for individual virtualization hosts.
Migration Settings: On Migration Settings tab, you can configure storage and virtual machine live migration settings for a Hyper-V host as shown in the figure 1.2 below.
Figure 1.2: Storage and Virtual Machine Live Migration Settings for a Hyper-V Host
Here are the settings that you can configure for storage and virtual machine live migrations:
Maximum number of simultaneous live storage migrations: By default, concurrent storage live migration is 2.
Maximum number of simultaneous live migrations: By default, concurrent live virtual machine live migration is 2.
It is important to note that migration settings are collected by the VMM Agent when you add Hyper-V host under VMM management. By default, Hyper-V is configured with 2 concurrent storage live migration and 2 virtual machine live migrations when you enable the Hyper-V role on a Windows Server. Live storage migration is used to move virtual machine’s storage and live virtual machine migration is used to move a virtual machine within a Hyper-V cluster. In case you wish to increase the concurrent migrations, you can do so by specifying a value in the text box as shown in the screenshot above.
If you wish to configure concurrent migration settings from command prompt, you can run below PowerShell command on a Hyper-V host:
Set-VMHost -MaximumVirtualMachineMigrations 5 -MaximumStorageMigrations 7
Above command increases concurrent storage live migration to 7 and virtual machines live migration to 5.
When performing the virtual machine live migration, take a note of the following points:
You cannot multi-select virtual machines to perform live migration of virtual machines. You must manually start each live migration.
As per the default concurrent live migration settings, a Hyper-V host can participate in one outgoing and one incoming, two outgoing live migrations, or two incoming live migrations.
Storage and virtual machine live migrations are independent. You cannot perform two virtual machines live migrations and two storages live migrations simultaneously.
Although it is easy to set a value to increase the simultaneous migrations for both storage and virtual machine live migrations, but you need to be very careful when deciding a number. It is because setting an undesired value may cause poor Hyper-V host performance.
For virtual machine live migration, you can set performance options as explained below:
Standard Live Migration: This is the legacy TCP/IP option that is not optimized. You can use a NIC team for bandwidth aggregation.
Use Compression: Compression is the default performance option for Hyper-V host running Windows Server 2012 R2 and later operating systems. This option uses the idle CPU time to reduce the time to live migrate virtual machines. It is recommended that you use this option for virtual machine live migrations.
Use SMB as transport: This uses SMB 3.0 RDMA and Multichannel.
If you wish to modify virtual machine live migration performance option from command line, run below PowerShell command on a Hyper-V host:
Set-VMHost –VirtualMachineMigrationPerformanceOption SMB
There are two authentication protocols available for virtual machine live migration; CredSSP and Kerberos protocol. Although CredSSP requires no extra configuration, but it requires that you log on to source Hyper-V host to start a virtual machine live migration. Kerberos authentication protocol is more secure and is used by most of the organizations.
Last configuration item available on the Migration Settings tab is “Incoming live migration settings”. Since virtual machine live migration involves transferring virtual machine memory and its state, it is recommended that you configure and select a dedicated network with gigabit or faster speed.
We focused on Reserves and Migration Settings tabs in this article. As explained, by default, VMM configures a Hyper-V host to inherit host reserve settings from the VMM host group, but you can always configure host reserve settings for individual Hyper-V host by checking “Override host reserves settings from the parent host group” option on the Reserves Tab available on the property page of a Hyper-V host.
Starting with Virtual Machine Manager 2012 R2, you can perform faster virtual machine live migrations by selecting the suitable performance options as explained in this article. You can select compression or SMB as the performance option. By default, Hyper-V hosts are configured to use compression performance option which is best suited in many Hyper-V environments.
In the part 6 of this article series, we will explain Placement Paths, Virtual Switches, Servicing Window, and Custom Properties tabs.
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