qemu-virtualisation 101 with chatgpt

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What is virtualisation 
Virtualization is a technology that allows creating an abstraction layer on top of a physical server, network, or storage, allowing multiple virtual entities to run on the same physical hardware. This provides benefits such as increased utilization, reduced costs, improved scalability, and enhanced disaster recovery. There are different types of virtualization, including server virtualization, network virtualization, storage virtualization, and desktop virtualization.




Vijaykumar Jain
If I create two virtual machines, are they completed Isolated from each other
Yes, generally virtual machines are isolated from each other by default. They run on a virtualized environment, with each virtual machine having its own operating system, software, and applications, which are separate from those of other virtual machines. This provides the illusion of having multiple, independent systems running on a single physical machine, with each virtual machine operating as if it were a physical machine. However, this isolation can be configured differently depending on the virtualization platform and the specific use case, for example, you can configure network access between virtual machines or share storage resources.




Vijaykumar Jain
If there is 32gb ram on the host machine how much can I allocate to each of two vms
The amount of memory you can allocate to each virtual machine depends on several factors, such as the number of virtual machines running on the host machine, the memory requirements of each virtual machine, and the memory overhead of the virtualization platform.

As a rough estimate, you can allocate up to half of the host machine's memory (16GB) to each virtual machine, but this is not a hard and fast rule and you may need to adjust the allocation based on the specific requirements of your virtual machines. It's also important to keep in mind that there may be other system resources that need to be taken into consideration such as CPU, storage, and network bandwidth.

In summary, the exact amount of memory you can allocate to each virtual machine will depend on the specifics of your setup and the memory requirements of your virtual machines.




Vijaykumar Jain
Can I allocate 32gb ram to both the virtual machines when the host server has 32 gb ram
No, you can't allocate all 32GB of the host machine's memory to two virtual machines simultaneously. The virtualization platform itself requires some memory to run, known as the hypervisor overhead, and this will consume some of the host machine's memory. Additionally, the host operating system will also require some memory to run, and any other applications running on the host machine will also consume memory.

In general, it's recommended to leave some memory unused on the host machine to accommodate for these overhead requirements and to ensure that the host machine remains responsive and stable.

Therefore, in a 32GB host machine, you would typically allocate less than 32GB of memory to the two virtual machines combined, to ensure there is sufficient memory available for the host operating system, applications, and the virtualization platform. The exact amount will depend on the specifics of your setup, including the memory requirements of the virtual machines, the memory overhead of the virtualization platform, and the memory used by the host operating system and any other applications.




Vijaykumar Jain
Can I overcommit memory to ensure idle machines resources are used by other vms
Yes, you can overcommit memory in virtualization, which means allocating more memory to virtual machines than is physically available on the host machine. This is done with the expectation that not all virtual machines will use their full allocated memory simultaneously, and therefore, the host machine can effectively "overcommit" its physical memory to the virtual machines.

Overcommitting memory can be useful in cases where you have idle virtual machines and want to maximize the utilization of available memory. However, it's important to keep in mind that overcommitting memory can lead to performance degradation and potential stability issues if the virtual machines actually start using all the memory that has been allocated to them.

Therefore, overcommitting memory should be done with caution, and it's recommended to monitor the memory usage of virtual machines and the host machine closely to ensure that the virtualization platform is able to perform optimally and to avoid performance issues. It's also important to configure the virtualization platform to handle memory overcommitment gracefully, for example, by using memory ballooning or swap space, to ensure that virtual machines can continue to run even when the host machine is running low on memory.




Vijaykumar Jain
how to provision storage. i have 4 1TB disks attached to the host with raid10. how much disk should i allocate to the two vms.
The amount of disk space you should allocate to each virtual machine depends on the storage requirements of each virtual machine and your overall storage strategy.

When using RAID 10 with 4 1TB disks, you will have 2TB of usable storage space. This storage can be divided between the virtual machines in any way you see fit, based on their specific storage requirements. For example, you could allocate 1TB of storage to each virtual machine, or allocate more or less storage to each virtual machine as needed.

It's also important to keep in mind that the virtualization platform may have its own storage requirements and overhead, so it's important to factor this into your storage allocation calculations.

In summary, the exact amount of disk space you should allocate to each virtual machine will depend on the specifics of your setup, including the storage requirements of each virtual machine and the storage overhead of the virtualization platform. You can allocate disk space to the virtual machines as needed, to ensure they have enough storage to meet their requirements while also making efficient use of the available storage space.




Vijaykumar Jain
what is the difference between thin and thich provisioning. which is better in cases where servers reserves disk for future use but does not really use it
Thin provisioning and thick provisioning are two methods of allocating storage to virtual machines in a virtualized environment.

Thin provisioning involves allocating only the minimum amount of storage that is required for a virtual machine at a given time. The virtual machine can then grow its storage as needed, up to the limit set by the administrator. This allows for more efficient use of storage resources, as storage space is only used as it is needed, rather than being reserved in advance.

Thick provisioning, on the other hand, involves allocating all the storage that a virtual machine is expected to use up front. This means that the virtual machine has immediate access to all the storage it needs, but it also means that storage space is reserved for the virtual machine even if it is not currently being used.

In cases where servers reserve disk space for future use but do not actually use it, thin provisioning is usually the better option. Thin provisioning allows administrators to more efficiently allocate storage resources, as storage space is only used when it is needed, rather than being reserved in advance. This can result in significant cost savings and improved storage utilization, especially in environments where storage resources are scarce.

It's important to keep in mind that thin provisioning does require monitoring to ensure that virtual machines do not run out of storage space. This can be managed by using tools that provide alerts and reporting on storage utilization, as well as by regularly reviewing the storage utilization of virtual machines and adjusting the storage allocation as needed.




Vijaykumar Jain
should i create virtual devices on vms
It depends on the specific requirements and use case of your virtual machines.

Creating virtual devices, such as virtual disks or virtual network adapters, can provide several benefits, including:

Increased flexibility: Virtual devices can be added, removed, or reconfigured without affecting the underlying hardware, making it easier to change the configuration of a virtual machine as needed.

Improved manageability: Virtual devices can be managed and monitored in a centralized manner, making it easier to manage and maintain the virtual environment.

Enhanced security: Virtual devices can be isolated from the physical hardware, providing an additional layer of security and helping to prevent unauthorized access or tampering with the virtual environment.

However, creating virtual devices also has some disadvantages, including:

Increased overhead: Virtual devices can increase the overhead and complexity of the virtual environment, as the virtualization platform must manage the virtual devices in addition to the virtual machines.

Reduced performance: Virtual devices can result in a decrease in performance compared to physical devices, as the virtualization platform must perform additional processing to manage the virtual devices.

Whether or not to create virtual devices on virtual machines will depend on the specifics of your setup and the requirements of your virtual machines. In general, virtual devices are recommended in cases where increased flexibility, manageability, or security is required, while physical devices may be preferred in cases where performance is a primary concern.




Vijaykumar Jain
what is better hardware raid or software raid
The choice between hardware RAID and software RAID depends on a number of factors, including performance, reliability, cost, and complexity.

Hardware RAID uses dedicated hardware controllers to manage disk arrays, which can provide better performance and reliability compared to software RAID. Hardware RAID controllers also typically include a battery backup or capacitor to protect against data loss in the event of a power outage.

Software RAID, on the other hand, uses software running on the server's CPU to manage disk arrays. Software RAID is typically less expensive than hardware RAID, as it does not require dedicated hardware controllers. However, software RAID can be less reliable than hardware RAID, as it is subject to the performance and stability limitations of the underlying server hardware and software.

In general, hardware RAID is recommended for critical applications that require high performance and high levels of reliability, while software RAID may be suitable for less critical applications, or for environments where cost is a primary concern.

It's important to keep in mind that both hardware and software RAID have their own advantages and disadvantages, and the best choice will depend on the specifics of your setup, including your performance, reliability, cost, and complexity requirements. It's recommended to consult with a specialist or to perform thorough testing and evaluation before making a decision.




Vijaykumar Jain
i need to create a virtual interface on the vm and also limit its bandwidth usage to 1GB/s. the physical interface on the host has 10GB/s capacity. how to regulate bandwidth on vm
To limit the bandwidth usage of a virtual interface on a virtual machine (VM), you can use network shaping or traffic shaping techniques. Network shaping allows you to regulate the amount of network bandwidth that a virtual interface can use, ensuring that it does not consume more than the specified amount of bandwidth.

There are different ways to shape network traffic on virtual machines, including:

Using the virtualization platform's built-in features: Some virtualization platforms, such as VMware vSphere or Microsoft Hyper-V, have built-in features that allow you to shape network traffic for virtual interfaces.

Using a software-based network shaping tool: There are several third-party network shaping tools, such as tc, that can be installed on the host or the virtual machine to shape network traffic. These tools can be used to limit the bandwidth of a virtual interface to a specified amount, such as 1 GB/s.

Using hardware-based network shaping: Hardware-based network shaping solutions, such as routers or switches, can be used to regulate the bandwidth of virtual interfaces. These solutions can be more reliable and scalable than software-based solutions, but they can also be more expensive.

It's important to keep in mind that network shaping can affect the overall performance and availability of the virtual environment, and it may also introduce latency and jitter in the network. It's recommended to thoroughly test and evaluate the network shaping solution to ensure that it meets your performance and reliability requirements.




Vijaykumar Jain
what kind of issues do virtualization machines have compared to baremetal servers. 
Virtualization has many benefits, but it can also introduce some challenges compared to running workloads on bare metal servers. Some common issues with virtualization include:

Performance Overhead: Virtualization introduces additional overhead compared to running workloads directly on physical hardware. This can result in lower performance compared to running workloads on bare metal servers, especially for CPU-intensive or I/O-intensive workloads.

Resource Contention: Virtualization environments can lead to resource contention, especially when multiple virtual machines are running on the same physical host. This can result in reduced performance and unpredictable behavior.

Complexity: Virtualization introduces additional layers of abstraction and management, making the overall environment more complex compared to running workloads on bare metal servers. This can result in increased administrative overhead and make it more difficult to troubleshoot and resolve issues.

Security Concerns: Virtualization can introduce security concerns, such as the risk of hypervisor compromise, or the risk of virtual machines interfering with each other.

Licensing Costs: Some virtualization platforms require licenses, which can add to the cost of running virtual machines compared to running workloads on bare metal servers.

These challenges can be mitigated through proper planning, design, and management of virtual environments, as well as by choosing the appropriate virtualization platform and hardware. The choice between virtualization and bare metal servers will depend on the specific requirements and constraints of your workloads and infrastructure.




Vijaykumar Jain
what is qemu. can i create a vm using qemu
QEMU is a free and open-source machine emulator and virtualizer. It is often used as a virtualization solution for testing, development, and educational purposes. With QEMU, you can create virtual machines (VMs) and run different operating systems and applications within those VMs, just like you would on physical hardware.

Yes, you can create a virtual machine using QEMU. It supports various virtualization technologies, including full virtualization, para-virtualization, and hardware-assisted virtualization. You can create virtual machines with different operating systems, such as Windows, Linux, or macOS, and run them on different host operating systems, including Linux and Windows.

QEMU provides a command-line interface for creating and managing virtual machines. It can also be used in conjunction with other virtualization management tools, such as libvirt, for easier management and automation.

In summary, QEMU is a versatile virtualization solution that allows you to create virtual machines and run different operating systems and applications on them.




Vijaykumar Jain
i need to create a linux vm from ubuntu iso with 2GB ram, 2 cpu, 1 bridged adapter, 1 host only adapter, and 2 disks of 10GB each. what are qemu commands i need to run to create a vm for this
Here is an example of the QEMU command you would use to create a Linux virtual machine from an Ubuntu ISO with the specified configuration:

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qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-net nic,model=virtio,macaddr=52:54:00:12:34:56 \
-net bridge,br=br0 -net nic,model=virtio,macaddr=52:54:00:12:34:57 \
-net user,id=net0 -device virtio-net-pci,netdev=net0 \
-hda disk1.qcow2 -hdb disk2.qcow2 \
Explanation of the options used in the command:

-enable-kvm: Enables hardware-assisted virtualization, which can improve performance.
-m 2G: Specifies 2 GB of RAM for the virtual machine.
-smp 2: Specifies 2 virtual CPUs for the virtual machine.
-cdrom ubuntu.iso: Specifies the Ubuntu ISO file to use for booting the virtual machine.
-net nic,model=virtio,macaddr=52:54:00:12:34:56: Adds a virtual network adapter to the virtual machine with the specified MAC address and using the VirtIO model.
-net bridge,br=br0: Connects the virtual network adapter to the host's br0 bridge interface.
-net nic,model=virtio,macaddr=52:54:00:12:34:57: Adds another virtual network adapter to the virtual machine with the specified MAC address and using the VirtIO model.
-net user,id=net0: Creates a host-only network for the virtual adapter.
-device virtio-net-pci,netdev=net0: Connects the virtual network adapter to the host-only network.
-hda disk1.qcow2: Adds a virtual disk image with the specified file name for the first disk.
-hdb disk2.qcow2: Adds another virtual disk image with the specified file name for the second disk.
Note: The above command is just an example and may need to be adjusted based on your specific environment and requirements. You should also replace the ISO file path, disk image names, and bridge interface name with the appropriate values for your setup.




Vijaykumar Jain
i also want to bootstrap a script to install the packages on the vm. does qemu have a support of running a script post vm is created
Yes, QEMU allows you to run a script after the virtual machine has been created by using the -initrd or -kernel options to specify the script file to be executed after boot.

Here's an example of how you could modify the previous command to run a script after the virtual machine has been created:

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qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-kernel /path/to/kernel -initrd /path/to/initrd \
-append "console=ttyS0 bootscript=file:/path/to/script.sh" \
-net nic,model=virtio,macaddr=52:54:00:12:34:56 \
-net bridge,br=br0 -net nic,model=virtio,macaddr=52:54:00:12:34:57 \
-net user,id=net0 -device virtio-net-pci,netdev=net0 \
-hda disk1.qcow2 -hdb disk2.qcow2
Explanation of the new options:

-kernel /path/to/kernel: Specifies the Linux kernel to be used for booting the virtual machine.
-initrd /path/to/initrd: Specifies the initrd image to be used for booting the virtual machine.
-append "console=ttyS0 bootscript=file:/path/to/script.sh": Specifies the parameters to be passed to the kernel at boot time. In this case, we are specifying that the virtual machine should use the first serial console (console=ttyS0) and that a script located at /path/to/script.sh should be executed after boot.
Note that the kernel and initrd image specified must be compatible with the Ubuntu ISO you are using and that you may need to modify the script to fit your specific needs.




Vijaykumar Jain
i also need to mount the host directory into the guest vm to be able to run the script. how to enable that using qemu
You can mount a host directory into the guest virtual machine by using the -virtfs option in QEMU.

Here's an example of how you could modify the previous command to mount a host directory /host/path as /guest/path in the virtual machine:

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qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-kernel /path/to/kernel -initrd /path/to/initrd \
-append "console=ttyS0 bootscript=file:/guest/path/script.sh" \
-net nic,model=virtio,macaddr=52:54:00:12:34:56 \
-net bridge,br=br0 -net nic,model=virtio,macaddr=52:54:00:12:34:57 \
-net user,id=net0 -device virtio-net-pci,netdev=net0 \
-hda disk1.qcow2 -hdb disk2.qcow2 \
-virtfs local,path=/host/path,mount_tag=host_path,security_model=none,readonly
Explanation of the new options:

-virtfs local,path=/host/path,mount_tag=host_path,security_model=none,readonly: Specifies that the host directory /host/path should be mounted in the virtual machine as /guest/path with the tag host_path, with no security model, and in read-only mode.
Note that you may need to modify the bootscript and mount_tag options to fit your specific needs. You should also make sure that the host directory is readable by the user running the QEMU process.




Vijaykumar Jain
but downloading the packages requires a connection to the internet. do the adapter i make use of allow me to connect to the internet on the host machine from within in a vm
Yes, with a bridged adapter, you should be able to connect to the internet from within the virtual machine.

The bridged adapter is connected to the host machine's network interface and acts as an independent network device on the same network as the host. This allows the virtual machine to have its own IP address and direct access to the internet through the host machine's network connection.

However, the specific details of setting up network connectivity and allowing access to the internet from within a virtual machine can vary depending on your network configuration, so it's recommended to consult the documentation of your virtualization software or consult with a network administrator for more information.




Vijaykumar Jain
how to configure nat for my vm
NAT (Network Address Translation) can be used to provide internet connectivity to a virtual machine by allowing it to share the host machine's IP address. To configure NAT in a virtual machine, you need to perform the following steps:

Create a virtual network interface on the host machine that will be used for NAT:
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$ sudo ip tuntap add dev tap0 mode tap
$ sudo ip link set tap0 up
$ sudo ip addr add 192.168.100.1/24 dev tap0
Start the virtual machine with the following options, which will create a virtual network interface for the virtual machine that is connected to the host's tap0 interface:
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qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-netdev tap,id=net0,ifname=tap0,script=no,downscript=no \
-device virtio-net-pci,netdev=net0,mac=52:54:00:12:34:56
Set up NAT on the host machine to allow the virtual machine to access the internet:
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$ sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
$ sudo iptables -A FORWARD -i eth0 -o tap0 -j ACCEPT
$ sudo iptables -A FORWARD -i tap0 -o eth0 -j ACCEPT
Note that these steps are just a basic example and may need to be modified to match your specific network configuration. It is also recommended to consult the documentation of your virtualization software and network administrator for more information.




Vijaykumar Jain
how to take a snapshot or clone the vm. can i used the snapshot to provision multiple vms with different ips
Taking a snapshot or cloning a virtual machine allows you to save the state of a virtual machine at a particular point in time and then use it as the basis for creating new virtual machines.

To take a snapshot of a virtual machine in QEMU, you can use the "savevm" command. For example, to take a snapshot of a virtual machine named "vm1", you can run the following command:

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$ qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-loadvm vm1-snapshot -snapshot
To clone a virtual machine, you can create a new virtual machine from the snapshot and then customize it as needed. For example, you can run the following command to create a new virtual machine based on a snapshot named "vm1-snapshot":

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$ qemu-system-x86_64 -enable-kvm -m 2G -smp 2 -cdrom ubuntu.iso \
-loadvm vm1-snapshot
Yes, you can use a snapshot to provision multiple virtual machines with different IP addresses. To do this, you can create a new virtual machine from the snapshot and then configure its network settings to use a different IP address.

Note that the specific steps for cloning a virtual machine or configuring network settings may vary depending on your virtualization software, so it's recommended to consult the documentation of your virtualization software or consult with a network administrator for more information.




Vijaykumar Jain
will the new vms be able to communicate among themselves with the host only adapter setup
Yes, the new virtual machines created from a snapshot or clone will be able to communicate with each other using the host-only adapter setup.

A host-only adapter is a type of virtual network adapter that allows virtual machines to communicate with each other and the host system, but does not allow them to connect to the external network. This type of adapter creates a virtual network that is only accessible from the host and the virtual machines, so the new virtual machines will be able to communicate with each other and with the host system using the IP addresses assigned to their host-only adapters.

However, keep in mind that the exact configuration of the host-only adapter and the virtual network it creates may depend on the virtualization software you are using, so it's recommended to consult the documentation of your virtualization software for more information.