VM snapshots and images
What it is
- A snapshot is a read-only, full point-in-time copy of one managed disk. It exists independently of the source disk and can create a new managed disk.
- An image is a VM blueprint used to create repeatable VMs. Azure Compute Gallery adds image versioning and regional replication for supported image workflows.
Why it exists
Snapshots help investigate or recover a disk state; images help build repeatable VM fleets. They solve different problems and should not be confused with a complete application backup or disaster-recovery plan.
Key ideas
- Recovery path: snapshot → create a new disk → attach it as a data disk or use it to create a replacement VM, depending on the scenario.
- Consistency: a snapshot is crash-consistent. Cleanly shut down or quiesce an application before using a snapshot as a VM recovery source when application consistency matters.
- One disk at a time: snapshots do not coordinate multiple disks. A database spread across disks needs a coordinated backup approach.
- Cost: snapshots are billed separately from their source disk, based on used data size. Delete unneeded snapshots under a controlled retention process.
- Generalized image: removes machine-specific information before a single template is deployed to many new VMs. Use the documented preparation process for the operating system.
Northwind example
Before an operating-system experiment, Maya snapshots Northwind’s test VM OS disk. If the test fails, she creates a replacement disk from the snapshot. For the production ordering database, she does not rely on independent disk snapshots; the team uses an application-aware backup approach and verifies restore order. For a new fleet of identical web VMs, it uses a prepared image and infrastructure-as-code instead.
How it fits (diagram)
Exam notes
- Snapshot = one disk copy at a point in time; it does not turn a running application into a coordinated backup.
- Use a generalized image for a reusable fleet; use Azure Backup for scheduled recovery protection.
Related
Path MOC · managed-disks · azure-vm · virtual-machine-scale-set
📘 Source: Microsoft Learn — Create a snapshot of a virtual hard disk