220-1101 Virtualization and Cloud Computing Practice Question
A system administrator needs to add a new virtual hard disk to a running virtual machine without powering it off. The hypervisor supports this capability. Which feature should the administrator use?
⚠ Common exam trap
Watch out — candidates often confuse 'hot plug' with 'live migration' because both involve changes to a running VM, but live migration moves the entire VM between hosts, whereas hot plug specifically adds or removes virtual hardware without powering off.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Hot plug
Hot plug (also called hot add) allows a system administrator to add a virtual hard disk to a running virtual machine without powering it off, provided the hypervisor and guest OS support it. This feature leverages the SCSI or SATA hot-plug capability, enabling the virtual controller to detect and enumerate the new disk dynamically. It is commonly used in VMware vSphere and Hyper-V environments to expand storage without downtime.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Hot plug
Why this is correct
Hot plug (or hot add) is a hypervisor feature that lets you attach a virtual disk to a powered-on VM without rebooting, eliminating downtime. It relies on ACPI-based device hot-add events, supported by SCSI or SATA controllers configured for hot-plug, and requires the guest OS to have hot-plug drivers (e.g., Windows `storport`, Linux `sd_mod`). The disk appears as a new device, and the OS can initialize it on the fly. This is the correct method for the requirement of zero downtime.
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Snapshots
Why it's wrong here
Snapshots preserve the exact state of a VM—including disk contents, memory, and power state—at a specific moment for rollback or backup. They do not modify the VM's hardware configuration or attach new devices. Taking a snapshot before a change is a safety measure, but the snapshot itself cannot add a virtual disk to a running VM. Using snapshots for hardware addition would be incorrect and could lead to confusion about the VM's current state.
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Thin provisioning
Why it's wrong here
Thin provisioning is a storage virtualisation technique that allocates space to a virtual disk only when data is written, rather than pre-allocating the full maximum size. It is a property of the virtual disk's backing file, not a mechanism for dynamically attaching new disks to a running VM. You could thin-provision a new disk when you create it, but you'd still need a hot-add operation to attach it while the VM runs. It addresses storage efficiency, not device insertion.
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Live migration
Why it's wrong here
Live migration moves an entire running VM from one physical host to another without network or service interruption, typically using shared storage and memory copying (e.g., vMotion). It preserves the VM's existing hardware configuration but does not add, remove, or modify any virtual devices. While it can be used for host maintenance, it has nothing to do with adding a virtual disk to the VM. In fact, adding a disk is a separate operation from migrating.
Go deeper
Related to this question
Learn chapter
Virtual Desktop Infrastructure (VDI)
Key term
Small Computer System Interface
Small Computer System Interface (SCSI) is a set of standards for connecting and transferring data between computers and peripheral devices like hard drives, scanners, and tape drives.
Key term
Serial Advanced Technology Attachment
Serial Advanced Technology Attachment (SATA) is a computer bus interface used to connect storage devices like hard drives and solid-state drives to a computer's motherboard.
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Written by Johnson Ajibi, MSc IT Security
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