VM Hardware

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1. Modifying VM Settings: Why Power State Matters

Virtual hardware behaves like real hardware in one important way: some components must exist before the computer turns on.

Powered Off Changes (Most Hardware)

When the VM is off, the hypervisor can safely rewire the virtual motherboard.

You typically must power off the VM to change:

  • RAM size
  • Number of CPU cores
  • Storage controllers
  • Adding or removing virtual hard disks
  • Virtual Chipset/Firmware: Changing between legacy BIOS and UEFI/EFI.

Why? Because the guest OS detects these at boot time, just like a real BIOS/UEFI scan.

Running Changes (Hot-plug Features)

Some components are designed to be hot-swappable:

  • Network adapter connection (plug/unplug the cable)
  • CD/DVD ISO files
  • USB devices
  • Hot-Add RAM/CPU (Advanced Feature): Some enterprise hypervisors (like VMware or KVM with specific configurations) allow adding or removing RAM/CPU while the VM is running, provided the Guest OS supports the ACPI signals correctly. This is rare in Type 2 hypervisors like VirtualBox.

These behave like plugging in a USB stick or Ethernet cable on a real computer.

2. CPU and RAM: The Performance Balancing Act

Your host OS and guest OS share the same physical hardware. Virtualization is not magic; it is negotiation.

RAM Allocation (System > Motherboard)

  • RAM assigned to the VM is reserved while the VM runs.
  • If you give too much RAM to the VM:
  • The host OS slows down
  • Everything becomes laggy

That green zone in VirtualBox is a safety buffer. Staying inside it keeps the host breathing comfortably. 🫁

Best practice:

  • Linux VMs: 1–2 GB for light tasks, 4 GB+ for desktops
  • Windows VMs: 4 GB minimum for usability
  • Less Common Topic: Memory Ballooning: Explain that Type 1 hypervisors use a "balloon driver" inside the guest to reclaim unused RAM back to the host when the physical system is under heavy load, which is more efficient than hard capping.

CPU Allocation (System > Processor)

  • Each VM “core” is a virtual CPU thread, not a physical core.
  • Assigning more cores:
  • Helps with compilation, compression, databases
  • Does not help much for single-threaded tasks

Execution Cap

This is a CPU speed governor:

  • 100% = VM can use full assigned CPU time
  • 50% = VM can only use half of its allowed CPU

This is useful on shared machines or labs where one VM must not dominate.

PAE/NX

  • PAE allows 32-bit OSs to access more than 4 GB RAM
  • NX helps with memory protection and security

Most modern OSs expect this to be enabled.

3. Virtual Storage: The VM’s Memory Palace

Virtual disks are just files on the host, but to the guest OS they look like real drives.

3.1 Storage Controllers Explained

The controller defines how the disk “connects” to the VM.

  • IDE
  • Old and slow
  • Used mainly for legacy OSs or CD/DVD drives
  • SATA
  • Default and reliable
  • Good compatibility and performance
  • NVMe
  • Simulates modern SSDs
  • Faster I/O, lower latency
  • Best for modern Linux and Windows guests
  • SCSI (LSI Logic/Paravirtualized SCSI):
  • Less Common Use Case: Often seen in enterprise hypervisors (VMware/Xen). Paravirtualized drivers (like VMXNET3 in VMware or virtio-scsi) offer superior I/O performance because the guest OS is "aware" it is virtualized and communicates more efficiently with the hypervisor, bypassing some traditional hardware emulation layers.

Choose SATA for compatibility, NVMe for performance.

3.2 Virtual Disk Formats: Why They Matter

Each format is like a suitcase built for a different airline.

  • VDI
  • Best choice for VirtualBox
  • Supports snapshots, resizing, encryption
  • VMDK
  • Good for moving VMs between VirtualBox and VMware
  • Common in enterprise environments
  • VHD/VHDX
  • Designed for Microsoft ecosystems
  • Ideal for Hyper-V and Azure
  • QCOW2
  • Advanced features like compression and snapshots
  • Mostly used with KVM/QEMU

Rule of thumb: Stay native unless you plan to migrate.

3.3 Fixed vs Dynamic Disks

This is about when disk space is reserved.

Dynamically Allocated

  • The file grows as data is written
  • A 50 GB disk with 5 GB used = ~5 GB on host
  • Ideal for labs and testing

Downside: The disk file expands in chunks, which can slightly reduce performance over time.

Fixed Size

  • Entire disk space reserved immediately
  • Faster and more predictable performance
  • Preferred for databases and servers

Trade-off: Uses full space even if mostly empty.

4. Adding a Second Virtual Disk: What Really Happens

When you add a new disk in VirtualBox:

  • The hypervisor creates a new disk file
  • It connects it to the virtual controller
  • The guest OS sees it as raw hardware

The OS does not automatically use it.

Inside the Guest OS (Linux Example)

  1. lsblk shows:
  2. sda → original system disk

  3. sdb → new, empty disk

  4. You must:

  5. Create a partition
  6. Format it (ext4, xfs, etc.)
  7. Mount it to a directory

This separation mirrors real-world system administration skills.

5. Display, Audio, and Network Tweaks

Display

  • Video Memory
  • Higher values allow higher resolutions
  • Important for GUI desktops
  • Graphics Controller
  • VMSVGA → Linux
  • VBoxSVGA → Windows
  • VBoxVGA (Legacy): Mention this is required for older 32-bit OSs or specialized configurations where VBoxSVGA fails.

Wrong choice = black screens or poor performance.

Audio

  • Disabling audio:
  • Saves CPU and RAM
  • Useful for server VMs
  • Advanced Use Case: Passthrough Audio: In some hypervisors (Type 1), it's possible to dedicate a physical sound card to a specific VM, bypassing the host entirely, though this is highly platform-dependent.

Network

  • Network adapters behave like virtual NICs
  • Mode (NAT, Bridged, Host-Only) defines how the VM talks to the world
  • Covered fully in the next session

6. Lab Exercises: What You Are Learning

Each lab task maps directly to real admin skills:

Resource Tuning

You learn:

  • Capacity planning
  • Performance trade-offs
  • Host vs guest resource management

Adding Storage

You learn:

  • Disk provisioning
  • Storage expansion without downtime (enterprise reality)
  • OS-level disk management

Disk Initialization

You practice:

  • Identifying block devices
  • Partitioning and formatting
  • Filesystem mounting

This is exactly what sysadmins do on cloud VMs every day.

7. Final Thought

Virtual machines are not fake computers. They are software-defined hardware. Once you understand that, configuring VMs stops being clicking menus and starts being engineering.

Reflection & Further Research 🧭

Reflection Questions

  1. If snapshots depend on the original VM disk, what happens if that disk is deleted?
  2. Why do hypervisors warn administrators about long-lived snapshots?
  3. In what scenarios would reverting to a snapshot be dangerous rather than helpful?
  4. How does snapshot usage differ between test environments and production systems?

Further Research Topics

Learners may explore one or more of the following:

  • Difference between full clone and linked clone
  • How snapshot delta disks affect I/O performance
  • Snapshot handling in different hypervisors (VirtualBox, VMware, Hyper-V)
  • Why enterprise environments limit snapshot retention
  • Relationship between snapshots, clones, and templates

Concept Bridge to Next Session

From Snapshots to Cloning

Snapshot
---------
One VM
One Timeline
Rollback-focused

Clone / Template
----------------
Multiple VMs
Independent Lifecycles
Scale-focused

Snapshots look backward. Clones and templates look forward.

First VM Network Modes