vm-snapshot

VM snapshots and images

What it is

• A snapshot is a read-only, full point-in-time copy of a managed disk, regionally stored, used for backup, or to build new disks.
• An image (shared image / managed image) is a generalized OS + apps blueprint you deploy many VMs from, backed by the Azure Compute Gallery for versioning and regional replication.

Why it exists

You need to recover a broken VM, or stamp out many identical VMs without reconfiguring each. Snapshots give cheap rollback; images give repeatable, versioned, regionally-replicated provisioning.

Key ideas

• Snapshot → new disk → attach to a VM; or snapshot both OS+data disk to reconstruct a VM. Snapshots of a running VM can be inconsistent unless the app is quieted.
• Generalization: Windows sysprep, Linux waagent -deprovision — removes machine-specific data so the image can be deployed to many VMs as if new.
• Managed image vs Compute Gallery: shared images in the Azure Compute Gallery support versioning (publisher:offer:sku:version) and replication to multiple regions → the modern path.
• Images + scale sets / Bicep → consistent fleet provisioning.

How it fits (diagram)

Exam notes

• Snapshot = disk-level backup; does not generalize — do not boot the same SID/hostname on many snapshots.
• To create a reusable fleet image: generalize first (sysprep/waagent), then capture image. Deploying the same image (not generalized) to many VMs causes identity conflicts.
• Azure Compute Gallery (formerly Shared Image Gallery) = versioned + globally replicated images, integrated with scale sets for patching.
• AZ-104: understand when to snapshot vs image vs Back up VM (Azure Backup) for disaster recovery.

Related

Path MOC · managed-disks · azure-vm · virtual-machine-scale-set

📘 Source: Microsoft Learn — Vm Snapshot