Introduction
When launching a new instance, you can select a boot source for the new instance in the Source window (see the picture below). There are four options you can select:
- Image
- Instance Snapshot
- Volume
- Volume Snapshot
The purpose of this document is to explain the differences between the options, so you can choose the best source for your new instance.
The Image option is the most common choice, as it uses the Nectar pre-built image as a base of an instance. The Instance Snapshot option lets you choose a snapshot of another instance as a kind of template for the new instance. The Volume and Volume Snapshot use volume storage as the base of the new instance.
Differences between boot sources
Due to the different implementations of the boot source types, Image and Instance Snapshot behave fairly similar to each other, but differently to the Volume and Volume Snapshot. The difference will be seen in what happens at instance deletion. The below lists what will happen to the boot source after deleting an instance:
- Image: After the instance is deleted, the root disk and ephemeral storage are both deleted and all data are not saved.
- Instance Snapshot: It behaves the same as the Image option, except any data saved before you taking the snapshot will still remain. Ongoing changes to your data after the instance is launched will not be saved.
- Volume: The new instance immediately saves all changes to the volume, and the volume will persist after instance creation. Therefore, your data will still remain even after instance is deleted. Note: if you have ephemeral storage attached to the instance, this data will not be saved when the instance is deleted. Only data saved in the root disk (volume) will remain. You should never store irreplaceable data on ephemeral storage.
- Volume Snapshot: This is a copy of a Volume. For the purposes of acting as the source for a new instance, a Volume Snapshot behaves the same as a Volume.
The volume source types are only relevant in projects which have volume storage quota. There is more about this type of quota in the following documentation:
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