Main Points
- Red Hat’s KVM virtualization offers high-performance enterprise-grade capabilities, including the ability to run hundreds of virtual machines on a single physical server.
- For KVM to perform optimally, it’s crucial to have the right hardware requirements, such as virtualization-enabled CPUs and enough memory.
- You can install KVM either during a fresh RHEL setup or add it to existing systems using a few commands.
- Red Hat’s KVM offers advanced networking options, ranging from simple NAT configurations to complex bridged setups suitable for enterprise environments.
- KVM provides flexible storage configuration, allowing it to use local disks, NFS shares, or enterprise SAN solutions based on your scalability requirements.
KVM and Red Hat Virtualization: A Powerful Enterprise Virtualization Solution
KVM (Kernel-based Virtual Machine) is at the heart of Red Hat’s virtualization strategy. It offers the performance of bare-metal with the flexibility of virtualization. KVM is an open-source technology that is fully integrated into the Linux kernel. It turns your Red Hat Enterprise Linux system into a powerful hypervisor that can host multiple virtual machines. Whether you want to consolidate servers, create development environments, or build a private cloud infrastructure, Red Hat’s KVM provides the performance, security, and scalability you need for production environments.
What sets Red Hat’s KVM apart is its smooth integration with the operating system. Unlike other virtualization solutions that install as a layer between hardware and the operating system, KVM is part of the Linux kernel itself. This design removes overhead and allows near-native performance for virtualized workloads. In addition, KVM uses hardware virtualization extensions (Intel VT or AMD-V) to further improve performance, making it suitable for even the most demanding enterprise applications.
Red Hat’s KVM supports both Linux and Windows guest operating systems, giving it the flexibility needed by today’s IT departments. It offers enterprise features such as live migration, storage management, and network resource control, while still being compatible with existing infrastructure investments. This guide will take you through the process of setting up and configuring KVM on Red Hat Enterprise Linux to create a powerful virtualization environment.
What You Need to Know About Hardware Before You Begin
Before you get started with installing KVM, it’s important to make sure your hardware meets the necessary requirements. Not all hardware supports virtualization effectively, and planning your environment properly is key to ensuring good performance and stability.
What Your CPU Needs for KVM Virtualization
KVM runs best when it can use your processor’s virtualization extensions. To make sure KVM runs efficiently, your CPU needs to support either Intel Virtualization Technology (VT-x) or AMD Virtualization (AMD-V) extensions. You can find these features in most processors made after 2006, but your system’s BIOS might have them turned off by default. To see if virtualization extensions are available and turned on, run grep -E ‘vmx|svm’ /proc/cpuinfo. If this command gives you output, your processor supports virtualization extensions.
When setting up a production environment, it’s wise to take into account that each virtual machine will need CPU resources. Therefore, it’s recommended to use multi-core processors with a minimum of 4 cores. Most enterprise deployments use servers with either dual-socket or quad-socket with a high number of cores to get the most VM density. Essentially, the more virtual machines you plan on running at the same time, the more CPU cores you’ll need to keep everything running smoothly.
Moreover, the latest processors come with features such as Extended Page Tables (EPT) for Intel or Nested Page Tables (NPT) for AMD, which greatly enhance memory management for virtual machines. These features lower the overhead related to memory virtualization and can offer significant performance advantages, particularly for workloads that are memory-intensive.
RAM Requirements for Host Machines
In most virtualization environments, the biggest bottleneck is often memory. As a general rule of thumb, the host machine should have enough physical RAM to run all the virtual machines, plus some extra for the host operating system. Red Hat suggests having at least 4GB of RAM for the host system, plus the total memory needed for all the virtual machines you plan to run.
Although KVM allows you to allocate more RAM to VMs than what is physically available, known as memory overcommitment, you should be careful when using it. This is because it can reduce performance when the host system needs to swap memory to disk. For production environments, it’s best to keep overcommitment ratios low and keep a close eye on memory usage.
Considerations for Storage to Maximize Virtual Machine Performance
Storage performance is a key factor in the overall performance of your virtual machine. To maximize performance, it is recommended to use dedicated SSDs or NVMe drives for your virtual machine storage. Traditional HDDs can be more cost-effective for large storage needs, but can become a bottleneck when running multiple virtual machines at the same time.
It’s important to think through your storage architecture. Local storage is simple and performs well, but it doesn’t offer the flexibility of shared storage solutions. Shared storage solutions like NFS, iSCSI, or Fibre Channel SANs allow for advanced features like live migration between hosts, but they require additional network infrastructure. For enterprise environments, a combination of fast local storage (for VM operating systems) and shared storage (for VM data) often provides the best balance of performance and flexibility.
Network Interface Needs
For a KVM virtualization host, it is crucial to have dependable network connectivity. At the very least, a single Gigabit Ethernet interface is necessary. However, most production environments use several network interfaces for segregation, redundancy, and performance. It may be beneficial to use separate physical interfaces for management traffic, virtual machine traffic, storage traffic (if you’re using network-attached storage), and live migration traffic.
Network interface bonding is an excellent way to improve throughput and redundancy, especially in high-availability environments. If you’re working with a large number of virtual machines or data-heavy workloads, consider using 10GbE, 25GbE, or faster network interfaces to avoid network congestion.
How to Install KVM on Red Hat Enterprise Linux
There are two ways to install KVM on Red Hat Enterprise Linux: during the initial OS installation or by adding packages to an existing system. Once you know what components and configurations are needed, both methods are easy to do.
Red Hat Enterprise Linux’s KVM hypervisor is made up of several essential components that collaborate to provide a comprehensive virtualization solution. The kvm kernel module is responsible for the core virtualization infrastructure, while user-space tools such as libvirt, virt-manager, and virsh offer management capabilities. QEMU rounds out the virtualization stack by providing device emulation for virtual machines.
Method for New Installation
If you’re doing a new installation of Red Hat Enterprise Linux, the best way to go about it is to select the “Virtualization Host” option during installation. This server profile will automatically install all the necessary packages and set up the system for virtualization workloads.
While you’re installing, you’ll be asked to set up network interfaces, storage, and other system settings. Be careful with storage setup, because it will affect how well your virtual machines work. If you can, use different storage volumes for the host system and virtual machine storage.
Once the installation is done, your system will restart and the KVM functionality will be ready for use. To confirm the installation, you can check if the required kernel modules have been loaded by typing lsmod | grep kvm. If you see both kvm and either kvm_intel or kvm_amd modules listed, this means the installation was successful. The type of module listed will depend on the type of processor you have.
How to Add KVM to Your Current RHEL Systems
For those who already have a Red Hat Enterprise Linux system, you can simply turn it into a virtualization host by installing the necessary packages. This can be done with just a few easy commands:
- First, install the virtualization group package with: sudo yum groupinstall “Virtualization Host”
- For additional management tools, install: sudo yum install virt-manager virt-viewer
- After installation, start and enable the libvirtd service: sudo systemctl start libvirtd && sudo systemctl enable libvirtd
- Finally, verify that KVM modules are loaded with: sudo lsmod | grep kvm
This approach is particularly useful when repurposing existing hardware for virtualization or when you need to maintain specific configurations from your current system. The virtualization packages integrate smoothly with the existing operating system without requiring a complete reinstallation.
Should you come across any problems while installing, make sure your computer meets the hardware requirements we discussed earlier, especially when it comes to CPU virtualization support. If your system’s BIOS doesn’t already have virtualization extensions enabled, you may need to turn them on.
Checking KVM Installation
Once you’ve installed KVM, you’ll need to check that your system is set up correctly for KVM virtualization. Use the virt-host-validate command to do a full check of your virtualization environment. This tool checks various parts of your system setup, such as CPU virtualization extensions, kernel modules, and IOMMU support.
When everything is set up correctly, you should see PASS
How to Check If Your KVM Installation Worked
Once you’ve finished the installation process, you’ll want to make sure that your system is set up correctly for KVM virtualization. To do this, run virt-host-validate. This will check a variety of different things about your system configuration, such as CPU virtualization extensions, kernel modules, and IOMMU support.
You want to see a PASS status for all critical checks. If you see any WARN or FAIL messages, you need to address those issues before proceeding. Some of the common issues are disabled CPU virtualization in BIOS or missing kernel modules. You can usually resolve these issues by adjusting BIOS settings or installing additional packages.
It’s also possible to check the status of the libvirt service using systemctl status libvirtd. The service should be in an active, running state. If it isn’t, you can restart it using sudo systemctl restart libvirtd and look for any error messages in the system logs with journalctl -u libvirtd.
Setting Up Your Network
Networking is key to any virtualization environment. KVM on Red Hat offers several different networking modes to fit your use case, from simple NAT configurations for development to complex bridged configurations for enterprise.
Standard NAT Network Configuration
When you install KVM, it automatically creates a NAT (Network Address Translation) network called “default.” This network allows virtual machines to connect to external networks while hiding behind the host’s IP address. The default network usually uses the 192.168.122.0/24 subnet and includes a DHCP server that automatically assigns IP addresses to virtual machines.
For most basic scenarios, this configuration is adequate and requires minimal setup. Virtual machines can access external networks, but without additional port forwarding rules, external systems cannot directly access the VMs. Use the command virsh net-list –all to verify that the default network is available. The default network should be active.
Should the default network not be running, you have the option to start it using virsh net-start default and make sure it starts automatically at boot using virsh net-autostart default. This will provide your virtual machines with consistent network connectivity every time the host system boots up. For further optimization, you can refer to this network configuration optimization guide.
Setting Up Bridged Networks
If you’re working in a production environment where you need your virtual machines to be on the same network as your physical hosts, you’re going to want to set up a bridged network configuration. Essentially, a bridge connects your virtual machines directly to your physical network. This allows them to get IP addresses from your physical network’s DHCP server and makes them accessible just like your physical machines.
If you want to set up a bridged network, the first thing you need to do is set up a network bridge on the host system. You can do this by either editing the network configuration files in the /etc/sysconfig/network-scripts/ directory or by using the nmcli tool. Here’s a simple example of how you can use nmcli:
# Create a bridge device sudo nmcli con add type bridge con-name br0 ifname br0 # Add your physical interface to the bridge sudo nmcli con add type bridge-slave con-name ens3-slave ifname ens3 master br0 # Configure the bridge with an IP address (if static addressing is used) sudo nmcli con mod br0 ipv4.addresses 192.168.1.10/24 ipv4.gateway 192.168.1.1 ipv4.dns 192.168.1.1 ipv4.method manual # Bring up the bridge connection sudo nmcli con up br0
After you’ve created the bridge on the host system, you’ll need to define a libvirt network that uses this bridge. You can do this by creating an XML configuration file and importing it with virsh, or using virt-manager to create a new network with the bridge device. This bridged configuration provides the most transparent network integration for virtual machines in enterprise environments.
Setting Up Virtual Networks with virsh
If you need a more complex or custom network setup, you can use the virsh command-line tool. It gives you a full range of network management features. You can make, change, and remove virtual networks with XML definition files. These files let you set network parameters like IP ranges, DHCP settings, and routing rules.
When you want to make a custom network, you need to start by creating an XML file with the network definition. Here’s an example of what a simple isolated network configuration might look like:
<network>
<name>isolated</name>
<bridge name="virbr1" />
<ip address="192.168.100.1" netmask="255.255.255.0">
<dhcp>
<range start="192.168.100.128" end="192.168.100.254" />
</dhcp>
</ip>
</network>
Save this definition to a file (e.g., isolated-network.xml) and then import it with virsh net-define isolated-network.xml. Start the network with virsh net-start isolated and enable autostart with virsh net-autostart isolated. This approach gives you complete control over network configurations and allows you to create multiple isolated networks for different purposes, such as separating development, testing, and production workloads.
Optimizing Network Performance
There are several ways to boost the network performance of your virtual machines. For workloads that require high throughput, you might want to use virtio network interfaces. These interfaces give you performance that is almost as good as native performance because they use paravirtualization. Virtio drivers let the guest and host systems communicate directly with each other, which reduces the overhead that comes with network virtualization.
For workloads that require a lot of network processing, enabling multiqueue on a network interface can greatly enhance performance. This is because multiqueue allows network processing to be spread out over several CPU cores. To turn on multiqueue for a virtual machine, you need to modify its XML configuration. You can do this by using the virsh edit vm-name command and adding the driver element with the queues attribute. For example, you might add <driver name=’vhost’ queues=’4’/> to the interface section. For more detailed guidance, you might find this network configuration optimization guide helpful.
For workloads that require a lot of resources, you can use technologies like SR-IOV (Single Root I/O Virtualization) to allow virtual machines to access network hardware directly. This bypasses the virtualization layer completely. Although it’s more complicated to set up, SR-IOV provides the best possible network performance for virtual machines. You’ll need supported network hardware and the right configuration on both the host and guest levels to use this approach.
Setting up Storage Pools
Storage is a key part of any virtualization setup, and it can have a big impact on the performance and reliability of your virtual machines. Red Hat’s KVM solution supports a range of different storage options, from basic file-based storage all the way up to enterprise-level SAN solutions. This means you can choose the storage solution that best fits your needs. For those interested in cloud solutions, here’s a Google Cloud migration guide that might be helpful.
Setting Up Local Disk Storage
The most basic storage setup involves using your server’s local disks to store the images of your virtual machines. KVM, by default, creates a storage pool in /var/lib/libvirt/images for the disk files of your virtual machines. This default setup is perfectly adequate for simple setups and testing environments, and it doesn’t require any additional configuration.
To enhance performance, it’s recommended to build dedicated storage pools on distinct physical disks or SSD devices. This will separate the I/O of the virtual machine from the host operating system, thus reducing competition and increasing overall performance. To create a new local storage pool using virsh, you need to prepare the directory first and then define the pool:
Setting up KVM Red Hat Virtualization involves several steps to ensure a smooth configuration process. First, you need to prepare your environment by installing the necessary packages and dependencies. Once the environment is ready, you can proceed with the installation of the KVM hypervisor. It’s essential to follow security best practices to protect your virtual machines from potential threats. After the installation, configure the network settings to enable communication between virtual machines and the host. Finally, test the setup to ensure everything is functioning as expected.
Setting up NFS Storage
If you need to share storage between multiple KVM hosts, NFS is a simple solution. NFS lets you store virtual machine images on a central server and access them from multiple hosts. This lets you do things like live migration without having to copy large disk files. It also makes managing your system easier and makes better use of resources across multiple hosts.
For setting up an NFS storage pool, you must have an NFS server that exports a directory with the right permissions. On the KVM host, use the following commands to define the storage pool:
Here’s how to create an NFS storage pool:
# Create an NFS storage pool sudo virsh pool-define-as nfs-pool netfs --source-host=nfs.example.com --source-path=/export/vmdata --target=/mnt/nfs-vms sudo virsh pool-start nfs-pool sudo virsh pool-autostart nfs-pool
If you’re setting this up for a production environment, you’ll want to make sure your NFS server is properly configured for performance and reliability. This might mean using NFSv4 with the right security settings, and tuning your NFS mount options for virtualization workloads. Parameters like rsize, wsize, and async can have a big impact on performance. And of course, you’ll want to make sure your network infrastructure between your KVM hosts and the NFS server can handle the I/O load you’re expecting. For more insights, you can explore Citrix Hypervisor security best practices to enhance your virtualization setup.
Integrating iSCSI Storage
iSCSI storage is a good option for businesses that need more performance than NFS can provide. It offers block-level access to shared storage resources. iSCSI storage is known for its good performance and reasonable cost, making it a popular choice for mid-range virtualization deployments. Unlike NFS, which shares files, iSCSI presents block devices to the host that can be formatted with any filesystem or used directly.
Setting up an iSCSI storage pool in KVM requires you to first install the necessary packages and configure the iSCSI initiator on your host system:
First, install the iSCSI initiator packages using the following command: sudo yum install iscsi-initiator-utils.
Next, you may need to configure the initiator name. You can do this with the following command: sudo vi /etc/iscsi/initiatorname.iscsi.
Finally, start and enable the iSCSI service with the following command: sudo systemctl enable --now iscsid.
Once you’ve discovered and logged into your iSCSI targets, you can create a storage pool using the detected iSCSI LUNs. You can do this through virsh or virt-manager. If you’re working with mission-critical workloads, you should consider implementing multipathing for redundancy and load balancing. iSCSI with MPIO (Multipath I/O) provides fault tolerance and can improve performance by distributing I/O across multiple network paths.
How to Use virt-manager for Storage Management
If you’re an administrator who prefers using graphical tools, you’ll find that virt-manager offers a straightforward interface for managing storage pools. To create or modify storage pools in virt-manager, simply open the application and go to “Edit” → “Connection Details” → “Storage” tab. This is where you can add new storage pools of different types, view existing pools, and allocate storage to virtual machines. For a more comprehensive understanding, you can refer to the Red Hat Enterprise Linux Virtualization Guide.
With virt-manager, you can easily carry out routine storage tasks such as creating new volumes, resizing existing ones, and keeping an eye on storage usage. Although you may still need to use command-line tools for more complicated storage configurations, virt-manager can take care of most daily storage management tasks. It’s important to note that any changes made in virt-manager will also show up in the underlying libvirt configuration, and vice versa. For a deeper understanding of virtualization tools, you might find this Parallels Desktop review insightful.
Setting Up Your Initial Virtual Machine
Now that your KVM environment is set up, it’s time to start creating virtual machines. Red Hat’s virtualization stack provides several ways to create VMs, ranging from easy-to-use graphical tools to robust command-line utilities that can be automated. We’ll look at the most frequently used methods.
1. Using the virt-manager GUI
The Virtual Machine Manager (virt-manager) provides a user-friendly graphical interface for creating and managing virtual machines. To create a new VM, launch virt-manager by typing sudo virt-manager in the terminal, then click the “Create a new virtual machine” button in the toolbar. The wizard will guide you through the process of selecting an installation source (ISO image, network installation, or existing disk image), allocating resources (CPU, memory, storage), and configuring network settings.
When you’re creating the virtual machine, make sure you look at the CPU configuration. To get the best performance, choose the “Copy host CPU configuration” option. This lets the host CPU features be used by the guest. This means the virtual machine can use advanced CPU features and instructions. When you’re deciding how much memory to give the virtual machine, think about what you need now and what you might need in the future. You can change the amount of memory later, but some guest operating systems don’t like it when the amount of memory changes. For more detailed guidance on setting up your virtual environment, refer to the Red Hat Virtualization Deployment and Administration Guide.
With Virt-manager, you can also personalize advanced options like virtual device models and boot order. For the majority of Linux guests, the virtio drivers offer the best performance for disk and network devices. For Windows guests, you may need to start with emulated devices and install virtio drivers after the initial setup. Finish the wizard to create and start your virtual machine, then connect to the console to start the operating system installation. For more tips on virtual machine customization, you can explore VM customization environment tips.
2. Creating VMs with the Command Line using virsh
For remote management or scripted deployments, you can use the virsh command-line tool to create and configure virtual machines. You usually create an XML definition file that specifies all the VM parameters and then import it with virsh. For a detailed review of virtualization tools, you can refer to this Parallels Desktop macOS virtualization review. Here is an example of how to create a basic virtual machine:
# Create a disk volume
sudo virsh vol-create-as default vm1.qcow2 20G --format qcow2
# Define the VM with an XML file
cat > vm1.xml << EOF
<domain type='kvm'>
<name>vm1</name>
<memory unit='GiB'>2</memory>
<vcpu>2</vcpu>
<os>
<type arch='x86_64'>hvm</type>
<boot dev='hd'/>
<boot dev='cdrom'/>
</os>
<devices>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/vm1.qcow2'/>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='file' device='cdrom'>
<source file='/path/to/your/rhel.iso'/>
<target dev='hdc' bus='ide'/>
</disk>
<interface type='network'>
<source network='default'/>
<model type='virtio'/>
</interface>
<graphics type='vnc'/>
</devices>
</domain>
EOF
# Define and start the VM
sudo virsh define vm1.xml
sudo virsh start vm1
# Connect to the VM console
sudo virsh console vm1
This approach is particularly useful for creating multiple similar virtual machines or for automating VM deployment in scripts. While the XML syntax can be complex, you can use existing VMs as templates by exporting their configuration with virsh dumpxml vm-name, modifying as needed, and defining new VMs with the modified XML. For more on virtualization, check out this Parallels Desktop macOS virtualization review.
3. Automated VM Deployment with Kickstart
If you need to deploy multiple Red Hat Enterprise Linux VMs with the same configuration, Kickstart is a powerful tool that can automate the process for you. The Kickstart files contain all the answers for an unattended installation, including partitioning, package selection, and post-installation configuration. This is a great way to create standardized environments on a large scale.
For KVM, you will need to create a Kickstart file with the configuration you want and make it available via HTTP, FTP, or local filesystem. You can then use virt-install with the –location and –initrd-inject options to specify the installation source and Kickstart file. For example:
sudo virt-install --name=ks-vm --memory=2048 --vcpus=2 \ --disk path=/var/lib/libvirt/images/ks-vm.qcow2,size=20 \ --location=http://mirror.example.com/rhel8/os/x86_64/ \ --initrd-inject=/path/to/kickstart.ks \ --extra-args="ks=file:/kickstart.ks console=ttyS0" \ --graphics none
This command will create a new virtual machine and boot it from the specified location. It will then inject the Kickstart file and perform an unattended installation based on your specifications. You can watch the installation progress on the console. Once it’s finished, the virtual machine will reboot and you’ll have a fully configured system. If you combine Kickstart with templates and scripting, you can quickly deploy and configure dozens or even hundreds of virtual machines without needing to manually intervene.
4. Bringing in Pre-existing VMs
If you’re moving from other virtualization platforms, you have the ability to bring pre-existing virtual machines into your Red Hat KVM environment. The virt-v2v tool makes it easy to convert from platforms such as VMware and Xen to KVM, taking care of necessary format conversions and driver changes. This tool is especially useful for businesses that are making the switch to Red Hat virtualization from proprietary platforms.
If you want to import a VMware virtual machine, you need to have access to the VMDK files or to the vCenter Server managing the VM. You should install the virt-v2v package, and then you can run a command like:
For more complex scenarios, such as importing from vCenter or importing Windows VMs, additional parameters may be required. The virt-v2v tool handles converting disk formats, adjusting boot configurations, and installing appropriate drivers for the target environment. After conversion, verify the imported VM’s configuration and make any necessary adjustments before putting it into production use.
Getting Started with Virtual Machine Management
Managing virtual machines effectively requires a solid understanding of the basic operations and tools Red Hat’s KVM implementation offers. By mastering these essentials, you can ensure your virtualization environment runs smoothly and efficiently.
Turning Virtual Machines On and Off
Whether you prefer graphical or command-line interfaces, you can manage virtual machines through both. The virsh command is a great tool for managing everyday tasks. Here are some basic commands for controlling the lifecycle of your virtual machine:
- virsh start vm-name – This command starts a virtual machine
- virsh shutdown vm-name – This command initiates a graceful shutdown
- virsh force-shutdown vm-name – This command forces a virtual machine to stop (equivalent to pulling the power cord)
- virsh reboot vm-name – This command reboots a virtual machine
- virsh suspend vm-name – This command pauses a virtual machine, freezing its state
- virsh resume vm-name – This command resumes a suspended virtual machine
For scheduling operations, you can combine these commands with system tools like cron or systemd timers. This lets you automate routine maintenance tasks, such as restarting services or performing scheduled reboots. Always prefer graceful shutdown methods when possible to prevent data corruption or filesystem inconsistencies within your virtual machines.
Using VM Snapshots for Backup and Recovery
VM Snapshots are a powerful tool for backup and recovery. They capture the state of a virtual machine at a specific moment in time. KVM supports both internal and external snapshots. Each type of snapshot has different features and uses. Internal snapshots include the memory state and are stored within the disk image file. External snapshots are stored as separate files and offer more flexibility in terms of management.
If you want to create a snapshot of a running VM using virsh, you would use a command like this:
Before making any major changes to your virtual machines, such as software upgrades or configuration changes, it’s a good idea to create a snapshot. This way, if anything goes wrong, you can quickly revert back to the previous state using the command virsh snapshot-revert vm-name snapshot1. For production environments, it’s recommended to have a regular snapshot strategy in place, and to regularly clean up old snapshots to avoid using up too much storage and slowing down performance.
sudo virsh snapshot-create-as vm-name snapshot1 "Pre-upgrade snapshot" --disk-only --atomic
Duplicating Virtual Machines
By duplicating, you can create new virtual machines based on existing ones, which not only saves time but also ensures consistency. Red Hat’s KVM implementation supports several duplication methods, ranging from simple disk copying to full VM duplication with configuration modifications. The virt-clone tool provides a simple way to duplicate virtual machines:
For more complex scenarios, you can customize the cloning process by specifying different storage locations, network configurations, or other parameters. When cloning Linux VMs, remember to adjust system identifiers like hostnames and IP addresses to prevent conflicts. For Windows VMs, use sysprep before cloning to generate unique system identifiers. Tools like cloud-init for Linux or cloudbase-init for Windows can automate post-cloning configuration, making them ideal for environments that frequently deploy new VMs from templates.
sudo virt-clone --original vm-source --name vm-clone --auto-clone
Transferring VMs Between Different Hosts
Live migration is a powerful feature of KVM that lets you transfer a running virtual machine from one physical host to another with very little downtime. This is important for load balancing, hardware maintenance, and disaster recovery. For live migration to work, the hosts need to share storage (through NFS, iSCSI, or other shared storage solutions) and have compatible CPU configurations.
If you want to do a simple live migration using virsh, you should use the migrate command:
Use the following command to live migrate a virtual machine to another host:
sudo virsh migrate --live vm-name qemu+ssh://destination-host/system
In a production environment, you might want to add additional options to this command for better security and performance. For example, the –compressed option can help reduce network traffic, and the –persistent option ensures that the virtual machine’s configuration is kept on the destination host. Be sure to test live migration thoroughly in a controlled environment before implementing it in production, as the behavior and requirements can vary depending on your specific workloads. For more insights, you can refer to this Google Cloud migration guide.
Techniques to Optimize Performance
Getting the best performance out of KVM on Red Hat Enterprise Linux means fine-tuning different components to find the right balance between how resources are used and how well the virtual machine performs. You can make your system work much more efficiently overall with some well-placed tweaks, and you won’t have to resort to upgrading your hardware.
Understanding CPU Pinning and NUMA Awareness
In today’s age, servers with multiple sockets have a Non-Uniform Memory Access (NUMA) architecture. This means that the time it takes to access memory depends on the location of the memory relative to the processor. To ensure the best performance, the virtual CPUs of a virtual machine should be pinned to the physical CPUs within the same NUMA node as the memory allocated to the VM. This reduces the latency of memory access and improves the overall performance, especially for workloads that require a lot of memory.
When you want to pin a CPU, you need to modify the XML configuration of the VM. Use the command virsh edit vm-name to do this and then add the pinning configuration that you need. For instance, if you want to pin a VM’s vCPUs to physical CPUs 4-7, this is how you do it:
<vcpu placement='static'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='4'/> <vcpupin vcpu='1' cpuset='5'/> <vcpupin vcpu='2' cpuset='6'/> <vcpupin vcpu='3' cpuset='7'/> </cputune>
For larger environments, the numad daemon can automatically adjust NUMA placements for optimal performance. Enable and start numad with sudo systemctl enable –now numad, and consider using the –numad option with virt-install when creating new virtual machines. This approach ensures VMs are automatically placed optimally without manual configuration.
Settings for Overcommitting Memory
Overcommitting memory allows you to assign more memory to virtual machines than is physically available on the host, which increases the density of the VM. KVM uses methods like Kernel Same-page Merging (KSM) to find and consolidate identical memory pages across virtual machines. To enable and adjust KSM:
Here’s how to enable KSM:
# Enable KSM sudo systemctl enable --now ksmtuned
And here’s how to adjust KSM aggressiveness:
# Adjust KSM aggressiveness (higher values are more aggressive) sudo echo 10000 > /sys/kernel/mm/ksm/pages_to_scan sudo echo 10 > /sys/kernel/mm/ksm/sleep_millisecs
Keep in mind that while memory overcommitment can increase VM density, it should be used carefully in production environments. Excessive overcommitment can lead to performance degradation if the host needs to swap memory to disk. Monitor memory usage closely and adjust overcommitment ratios based on your workloads. For critical production workloads, consider using transparent huge pages (THP) to reduce memory management overhead and improve performance. Enable THP with the following command:
echo always > /sys/kernel/mm/transparent_hugepage/enabled
Optimizing Disk I/O
When it comes to virtual environments, storage performance can frequently be a limiting factor. However, there are a number of strategies you can use to enhance disk I/O performance for your virtual machines. One of the first things you should consider is the virtual disk cache mode in the VM configuration. The “writeback” mode can deliver good performance, but it may also risk data loss in the event of power failures. On the other hand, “writethrough” offers better data integrity, but at the expense of performance. If you’re dealing with critical workloads, you might want to consider using “writethrough” in combination with a battery-backed controller on the host, as this can offer both performance and reliability. For more in-depth tips on optimizing your virtual machine setup, you might find this network configuration optimization guide useful.
Change the I/O scheduler on both the host and guest systems for virtualization workloads. On the host, the “deadline” or “noop” schedulers often outperform the default “cfq” scheduler for virtualization workloads. Configure the scheduler with:
For the best performance, you might want to consider using disk formats that support thin provisioning and features such as discard/TRIM. The qcow2 format with discard enabled allows the guest to notify the host when blocks are no longer needed, improving storage utilization and performance over time. When creating disks with virt-install or virsh, specify –sparse to enable thin provisioning, and ensure the guest operating system is configured to use TRIM/discard for unused blocks.
Utilizing KVM virtio Drivers
Virtio drivers, also known as paravirtualized drivers, are a fantastic way to enhance performance. They allow for direct communication between the guest operating system and the hypervisor, reducing the overhead associated with virtualization. For Linux guests, the virtio drivers are already included in the kernel. However, for Windows guests, you will need to install the drivers separately, which can be found in the virtio-win package.
For the best performance, try to use virtio for disk, network, and balloon devices as much as you can. When you’re creating a VM, make sure to specify the right bus types:
Let’s run through an example of creating a VM with virtio devices. The following command creates a VM named vm1 with 2GB of memory, 2 vCPUs, a 20GB disk, and a network interface:
sudo virt-install --name=vm1 --memory=2048 --vcpus=2 \ --disk path=/var/lib/libvirt/images/vm1.qcow2,size=20,bus=virtio \ --network network=default,model=virtio
For existing VMs, you can modify the device configuration using virsh edit vm-name to change device types to virtio. This is particularly important for production workloads where performance is critical. Additionally, consider enabling other virtio features like multi-queue for network interfaces and persistent memory for applications that can leverage it.
Enhance Your Virtualization Experience
Red Hat’s KVM version offers a strong foundation for creating scalable, high-performing virtualization environments. From simple configurations to enterprise-level infrastructures, KVM on Red Hat Enterprise Linux’s power and flexibility allow you to satisfy a variety of virtualization needs while remaining compatible with existing systems and processes. As you progress on your virtualization path, consider exploring advanced features like nested virtualization, PCI passthrough, and integration with orchestration platforms to further improve the capabilities of your environment. For expert advice and support on your virtualization journey, trust the experienced team at Red Hat to help you design and implement the best virtualization solutions for your specific needs.
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