--- tags: - datacenter - l1 - flashcard-deck - virtualization --- [Portal](../../../../library/portal/index.md) | **Level:** [L1: Foundations](../../../../library/portal/levels.md) | **Topics:** [Virtualization](../../../../library/portal/topics.md) | **Domain:** Datacenter & Hardware id category difficulty tags question answer source_path virtualization/e4a1e6b75789 virtualization easy virtualization, hypervisor, types What is the difference between a Type 1 and Type 2 hypervisor? Type 1 (bare-metal) runs directly on hardware with no host OS — examples: ESXi, KVM, Xen, Hyper-V. Type 2 (hosted) runs on top of a host OS — examples: VirtualBox, VMware Workstation. Type 1 has lower overhead and is used in datacenters and cloud. Type 2 is used for development and testing.\n\nRemember: "Hypervisor = VM manager." Type 1 (bare metal): ESXi, Hyper-V, KVM. Type 2 (hosted): VirtualBox, VMware Workstation. training/library/topics/virtualization/primer.md virtualization/a26e790216e6 virtualization easy virtualization, kvm, linux What are the three components of the Linux virtualization stack? KVM (kernel module providing hardware-accelerated CPU and memory virtualization via /dev/kvm), QEMU (userspace hardware emulation for disks, NICs, USB, display), and libvirt (unified API and daemon for managing VMs — virsh, virt-manager, and Terraform all talk to libvirt).\n\nRemember: "VM vs Container: VMs virtualize hardware (heavy, isolated), Containers share the kernel (light, fast)."\n\nGotcha: Containers are NOT VMs — a kernel exploit escapes all containers. training/library/topics/virtualization/primer.md virtualization/f356a1f4e3b1 virtualization easy virtualization, virtio, performance Why should you always use VirtIO devices in production VMs? VirtIO is a paravirtualized framework where the guest explicitly cooperates with the hypervisor. Compared to fully emulated devices (e.g., e1000 NIC or IDE disk), VirtIO provides 2-10x better network performance and 2-5x better block storage performance because it avoids the overhead of emulating legacy hardware. training/library/topics/virtualization/primer.md virtualization/b95322ccd5f5 virtualization medium virtualization, virsh, commands What are the essential virsh commands for VM lifecycle management? virsh list --all (list VMs), virsh start/shutdown/destroy/reboot (power control), virsh suspend/resume (pause in memory), virsh console (serial console, Ctrl+] to exit), virsh dominfo/domblklist/domiflist (metadata, disks, NICs). shutdown sends ACPI signal (graceful), destroy is like pulling the power plug. training/library/topics/virtualization/primer.md virtualization/43a69e2f9a9f virtualization medium virtualization, storage, formats Compare raw and qcow2 VM disk formats. raw: no thin provisioning, no snapshots, best I/O performance — use for high-performance workloads. qcow2: supports thin provisioning (disk grows on demand), supports snapshots, good performance — use for general purpose. qcow2 is the default choice; raw is for when maximum I/O performance is critical. training/library/topics/virtualization/primer.md virtualization/480253b3bb8e virtualization medium virtualization, snapshots, management How do VM snapshots work and why are they not a substitute for backups? Snapshots create a chain of differential disk images capturing a point-in-time state (virsh snapshot-create-as, snapshot-revert, snapshot-delete). They are not backups because the chain degrades performance as it grows, they reside on the same storage as the VM, and they are meant for short-term rollback points (hours, not weeks). training/library/topics/virtualization/primer.md virtualization/7e144df43e36 virtualization medium virtualization, migration, live What are the prerequisites and steps for live migration of a VM? Prerequisites: shared storage (NFS, Ceph, GlusterFS) or use --copy-storage-all, same CPU architecture on both hosts, network connectivity, libvirtd on both hosts. Steps: memory pages iteratively copied to destination, VM briefly paused when dirty page rate converges, remaining state (CPU registers, device state) transferred, VM resumes on destination. Typical downtime: 10-200ms. training/library/topics/virtualization/primer.md virtualization/c2b840a8e41a virtualization hard virtualization, numa, pinning Why does NUMA-aware VM placement matter and how do you configure it? Modern multi-socket servers have Non-Uniform Memory Access — CPUs have fast local memory and slow remote memory (40-100ns extra latency per access). Pin a VM's vCPUs and memory to the same NUMA node using virsh vcpupin and virsh numatune --mode strict --nodeset 0. Cross-node access kills latency-sensitive workloads. training/library/topics/virtualization/primer.md virtualization/6c8b7cee856b virtualization hard virtualization, ballooning, memory How does memory ballooning work in virtualization? The virtio-balloon driver lets the hypervisor reclaim memory from guests dynamically. virsh setmem 2G --live inflates the balloon (guest sees less RAM, hypervisor reclaims the rest). virsh setmem 6G --live deflates it (gives memory back). The guest kernel handles the reduced memory by swapping or reclaiming cache. Maximum memory is set with virsh setmaxmem. training/library/topics/virtualization/primer.md virtualization/44f457152877 virtualization hard virtualization, esxi, vmware How does VMware ESXi differ from KVM in enterprise environments? ESXi is a proprietary Type 1 hypervisor (free tier available, features require vSphere license). It uses vCenter for multi-host management (equivalent to oVirt for KVM), VMFS or vSAN for storage (vs qcow2/raw), and vMotion for live migration. CLI access via esxcli and vim-cmd. \nKey difference: ESXi is a managed product with enterprise support; KVM is open-source with community tooling. training/library/topics/virtualization/primer.md --- ## Wiki Navigation ### Related Content - [VMware](../../../../library/topics/vmware/primer.md) (Topic Pack, L2) — Virtualization - [Virtualization](../../../../library/topics/virtualization/index.md) (Topic Pack, L2) — Virtualization