Snapshot vs image

[dcbrown16]

This seems like a basic question but I can't find an answer in these documents.
What is the difference between a snapshot and an image? You can create both from a disk, and use both to create VMs.

"A managed VM image contains the information necessary to create a VM, including the OS and data disks."
(from this page)

"A snapshot is a full, read-only copy of a VHD. "
(from https://docs.microsoft.com/en-us/azure/virtual-machines/windows/snapshot-copy-managed-disk)

These are the definitions provided, but the image creation doc shows how to create images from disks or, indeed, from snapshots. What are we adding when we do so? When creating a VM from either of these resources, it seems like we still have the freedom to specify the size, location, and so on.

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• ID: c95cf419-74ae-f6d1-5c3e-01f988fdd9c4
• Version Independent ID: 6dfe7480-2c45-2be9-3f3d-8ee97f62cc62
• Content: Create VM from a managed image in Azure
• Content Source: articles/virtual-machines/windows/create-vm-generalized-managed.md
• Service: virtual-machines-windows
• GitHub Login: @cynthn
• Microsoft Alias: cynthn

[mimckitt]

Thanks for the question! We are investigating and will update you shortly.

[Karishma-Tiwari-MSFT]

@dcbrown16 A VM Image contains an OS disk, which has been generalized and needs to be provisioned during deployment time. OS Images today are generalized. This is meant to be used as a “model” to quickly stamp out similar virtual machines, such as scaling out a front-end to your application in production or spinning up and tearing down similar development and test environments quickly.

A Snapshot contains an OS disk, which is already provisioned. It is similar to a disk today in that it is “ready-to-use”, but unlike a disk, the VHDs of a Snapshot are treated as read-only and copied when deploying a new virtual machine. A snapshot is a copy of the virtual machine's disk file at a given point in time, meant to be used to deploy a VM to a good known point in time, such as check pointing a developer machine, before performing a task which may go wrong and render the virtual machine useless.

[dcbrown16]

Thanks @Karishma-Tiwari-MSFT , that will be very helpful in communicating to our customer for this case!

[v-maroge]

@Karishma-Tiwari-MSFT How far of settings can an image hold? (i.e. Programs installed and settings in OS such as Java, language program, and etc... I believe snapshots can save all of these)

[Karishma-Tiwari-MSFT]

@v-maroge An image of a virtual machine is a copy of the VM which encompasses the full definition of virtual machine’s storage, containing the OS disk, all data disks, data files and applications. It captures the disk properties (such as host caching) you need in order to deploy a VM in a reusable unit.

[Karishma-Tiwari-MSFT]

@v-maroge Does that answer your question?

[v-maroge]

@Karishma-Tiwari-MSFT The applications that are also contained in the image, will the they also be generalized (I'm imagining something like initialization), or will the data(or settings) in the application also be saved at the point the image was created?

[Karishma-Tiwari-MSFT]

It depends on lot of factors like the application, it's location in the VM, how the image was created etc. User specific settings are mostly generalized.
Since this is not specific to this doc, we will now close this issue. If there are further questions regarding this matter, please reach out in the forums and we will gladly continue the discussion.