Google Compute Engine: what is the difference between disk snapshot and disk image?

Question

I've been using both for my startup and to me, the functionality is the same. Until now, the instances I've been creating are only for computation. I'm wondering how GCE disk images and snapshots are different in terms of technology, and in which situation it is better to use one over the other.

Answer 1

A snapshot reflects the contents of a persistent disk in a concrete instant in time. An image is the same thing, but includes an operating system and boot loader and can be used to boot an instance.

Images and snapshots can be public or private. In the case of images, public can mean official public images provided by Google or not.

Snapshots are stored as diffs (a snapshot is stored relative to the previous one, though that is transparent to you) while images are not. They are also cheaper ($0.03 per GB/month vs $0.085 for images).

These days the two concepts are quite similar. It's now possible to start an instance using a snapshot instead of an image, which is an easy way of resizing your boot partition. Using snapshots may be simpler for most cases.

Answer 2

Snapshots:

• Good for backup and disaster recovery
• Lower cost than images
• Smaller size than images since it doesn't contain OS, etc.
• Differential backups - only the data changed since the last snapshot is recreated
• Faster to create than images
• Snapshots are only available in the project they are created (now it is possible to share between projects)
• Can be created for running disks even while they are attached to running instances

Images:

• Good for reusing compute engine instance states with new instances
• Available across different projects
• Can't be created for running instances(unless you use --force flag)