Calculate virtual size of image¶
https://blueprints.launchpad.net/glance/+spec/calculate-virtual-size
‘virtual_size’ should be set on image to avoid running qemu_img operations on consumer nodes.
Problem description¶
Image has virtual_size field in images table but it is never set unless we use taskflow introspect to create image. Consumers of glance like nova or cinder never consume image before calculating virtual size, which means every time they call for image, they need to perform qemu_img info call to calculate the virtual size of the image.
Use Case:¶
‘virtual_size’ should be set on image to avoid running qemu_img operations on consumer nodes.
Proposed change¶
All supported sparse disk image formats (i.e. what glance calls disk_format) simulate a larger virtual disk than the actual data that is stored, and record that virtual size in metadata. We propose to add a handler for each of the formats that can examine the chunks while streaming the image to extract the relevant metadata to determine the virtual disk size.
In glance, users can create images using two ways. 1) Create image API 2) Import image API
With this change virtual size will be set to image even user tries to use any of above two methods to create the image. Also images created by nova (nova-snapshot except ‘direct-to-backend snapshot’) or cinder (volume-upload-to-image) will be able to set the virtual size to image as well.
NOTE: To start with we are going to calculate virtual size for images which
will have container-format bare or other uncompressed formats only.
Later as and when required or expected we will enhance it for other
container-formats.
We will be performing this operation during uploading image data to glance store, so for image import this will happen during the actual import phase and not the stage phase.
Alternatives¶
None
Data model impact¶
None
REST API impact¶
None
Security impact¶
None
Notifications impact¶
None
Other end user impact¶
None
Performance Impact¶
None
Other deployer impact¶
None
Developer impact¶
None
Implementation¶
Assignee(s)¶
- Primary assignee:
danms
- Other contributors:
None
Reviewers¶
- Core reviewer(s):
abhishek-kekane jokke rosmaita
- Other reviewer(s):
whoami-rajat
Work Items¶
Add handler for each of the disk-format
Add wrapper around chunked reader to calculate virtual size
Add unit tests for coverage
Add functional tests
Dependencies¶
None
Testing¶
Tempest test to verify that virtual size is set on image using glance, nova snapshot and cinder upload-to-image operations.
Documentation Impact¶
Please refer to ‘Other deployer impact’
