Cloned from launchpad blueprint https://blueprints.launchpad.net/glance/+spec/split-image-size.

Description:

Currently, Glance's image have a size attribute which is being misunderstood and overloaded.

Image's size can refer to either the file size or the actual image size, which in cases like qcow2 may not be the same. This blueprint proposes splitting current size attribute in 2 separate attributes: image_size and file_size. The former refers at the real size of the image and the later at the actual size of the uploaded file. In most of the cases both fields will hold the same value, however, the number of cases where they may differ is as well big.

This blueprint considers both fields important for an image but not exactly required for it to exist. The image_size will allow users to know what is the actual size of the image and how much space the need to reserve in order to use it - cinder blocks allocation, for example. The file_size instead is necessary to support quotas, CLI progress bars, rate-limits, meetering and others.

It is possible to argue the need of this blueprint by saying that the actual image size could be part of the image properties / metadata. However, it is important to remember that image_size is a first citizen attribute in most of the external tools. Also, an attribute will ease the consumption of its value from Nova, Cinder and other tools relying on it.

Specification URL (additional information):

None