Last Updated: 2023-09-04

Hyperconverged Infrastructure (HCI)

Your resources: compute, storage, networking.

HCI: uses software to abstract, pool and manage those resources. (i.e. just another term for virtualized / software-defined compute, storage and networking.)

  • virtualized computing: hypervisor
  • virtualized storage: software defined storage (SDS)
  • virtualized networking: software defined networking (SDN)

Computation / Server Virtualization

3 kinds:

  • Full Virtualization (HVM): uses a hypervisor, which directly communicates with a physical server's disk space and CPU. Each virtual server is independent and unaware of the other virtual servers.
  • Para-Virtualization (PV): uses a hypervisor, each OS on the virtual servers is aware of one another.
  • OS-Level Virtualization (Containers): does not use a hypervisor. The virtualization capability is part of the physical server OS (e.g. cgroup).


Hypervisor = Virtual Machine Manager (VMM).

2 Types:

  • Type-1: native or bare metal hypervisor.
    • hypervisor runs directly on the host's hardware.
    • e.g. XEN, Hyper-V (Windows; used by WSL), VMware ESXi (renamed from ESX; i for integrated)
  • Type-2: hosted hypervisor.
    • hypervisor runs on a conventional operating system, a guest operating system runs as a process on the host.
    • e.g. VMware Workstation, VirtualBox, QEMU.

KVM can be considered as both Type-1 and Type-2.

Some of the most popular hypervisors:

  • Xen: an external hypervisor; it assumes control of the machine and divides resources among guests.
  • KVM: part of Linux and uses the regular Linux scheduler and memory management. This means that KVM is much smaller and simpler to use; it also provides some features not available in Xen. For example, KVM can swap guests to disk in order to free RAM.
    • It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko.
    • QEMU is the default VMM (Virtual Machine Manager) of KVM, but can be replaced. QEMU is a generic and open source machine emulator and virtualizer. The Android emulator is built on QEMU.
    • KVM: kernel side; QEMU: userspace. QEMU can use KVM and host CPU to accelerate: $ qemu-system-x86_64 accel=kvm ...
    • The kernel component of KVM is included in mainline Linux, as of 2.6.20. The userspace component of KVM is included in mainline QEMU, as of 1.3.
  • VirtualBox: by Oracle
    • a Type 2 Hypervisor.
    • open source and free; No hardware virtualisation required.
  • Cloud Hypervisor: a special-purposed VMM, doesn't aim to be a all-functioning emulator (like QEMU), but only concerns the use case of cloud workloads.

Used in clouds:

  • AWS:
    • Xen
    • Nitro Hypervisor: a modified KVM. For new kinds of EC2 instances.
  • Google:
    • GCE: KVM
    • Cloud Run: gVisor
  • Azure: Windows Hyper-V
  • VMware: ESXi
  • Oracle VM: Xen
  • Redhat: Red Hat Virtualization (RHV), based on KVM.

Live Migration

KVM has included LM (Live Migration) for over a decade.

KubeVirt has been supporting Live Migration functionality out of the box since CY2020 (see https://kubevirt.io/2020/Live-migration.html)

Azure: https://docs.microsoft.com/en-us/azure/virtual-machines/maintenance-and-updates

Paravirtualization(PV) vs Hardware Virtual Machine (HVM)

  • Paravirtualization: guest OS knows that it is running on a hypervisor instead of base hardware, recognizes that other virtual machines are running on the same machine
  • Hardware Virtual Machine (HVM): guest OS thinks that it is running directly on the hardware

Xen supports 2 virtualization types; Amazon supports 2 types as it runs on Xen.


  • An OS or Kernel called Hypervisor is installed on the hardware.
  • Dom0 is called the "privileged domain" which can issue commands to the hypervisor.


  • Stability/Performance is close to the real servers and hardware virtualization.
  • Overhead is very low.


  • Implementation is tough.
  • Both the host & guest kernels has to be patched.
  • Supports Linux only.
  • can’t change the OS options during install.
  • Can’t compile and install a custom kernel.


  • Stands for Hardware-assisted virtual machine.
  • Provides complete hardware isolation. The hardware provides support to run independently for each OS.


  • Can run Linux and Windows.
  • Complete secure hardware isolation.
  • Resembles close to a physical server.
  • Greater stability.


  • Low performance, because of the overheads at the hardware level.

Software Defined Networking (SDN)


  • a communications protocol, allows a server to tell network switches where to send packets.
  • used between the switch and controller on a secure channel.
  • program data plane, to allow control plane to scale separately from data plane.
  • an enabler of SDN.

Software-defined host networking stack: essentially an alternative to the kernel TCP/IP stack and the BSD stream sockets interface.

Google B4 is SDN. Google owned data centers are currently connected by B4, very high bandwidth but lower cost than B2, topology is restricted. B2 connects all, including 3rd party and PoP. (B4 is the 8-lane interstate freeway, B2 is 2-lane the highway)

Software Defined Data Center (SDDC)

Redfish: specs for APIs.

E.g. Netapp ONTAP: Compute nodes are all RedFish API-compatible.

Virtual Firewall

Palo Alto Networks vsys: Each virtual system (vsys) is an independent, separately-managed firewall with its traffic kept separate from the traffic of other virtual systems.