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Image in OpenStack is a shared and common file which binds to all instances or each VM have a copy of that in it's disk?

My question is about Image processes that happen when we select Launch machine, I create and upload my base image (ex. CentOS), and want to create an instance from that, Compute node get user request , nova-compute have cached image or ask from glance about image location, get the url of my image, then what happen? It copy base image for new instances? Or because OS in all VMs is repetitious, for saving disk space and …, use base image for number of instance and bind launched machines to it, save next changes to a new files in instances, so all new instances are combination of a point to base image and files (anything except of OS) which have the changes. As I learned any VM have .img file consist of OS, data (pics, files, application installed and ...) It means that compute node copy base image to new ephemeral space, boot machine from it and extend it by new change? So base image is only for copy from it and not bind to new instances. Is it correct?

I learned Compute Cache image which received from Glance, Actually I wanted to know more about after caching image in compute node, when launching VM, what happen! 1- Compute node give a copy of image to each new machine, and create .img for them? OR 2- all new machine use one shared base image, so in each VM disk only have just changes with a point to base image? For example I have one image CentOS that as last request cached to compute node, now a user requests 3 new centos VMs, 1-compute node copy 3 times from cached image and give them to new 3 VMs? OR 2- we have one cached common shared image between all 3 VMs? Naturally, if the answer is 2, we save disk space but I should be concerned about losing that shared image and I/O ps. 1 or 2 is correct?

I think we can check the size of new launched VMs, if it is equal or bigger than base image, it shows it have a copy of image in its disk. But unfortunately I do not have access to a VM launched.

Image in OpenStack is a shared and common file which binds to all instances or each VM have a copy of that in it's disk?

Hi All

My question is about Image processes that happen when we select Launch machine, I create and upload my base image (ex. CentOS), and want to create an instance from that, Compute node get user request , nova-compute have cached image or ask from glance about image location, get the url of my image, then what happen? It copy base image for new instances? Or because OS in all VMs is repetitious, for saving disk space and …, use base image for number of instance and bind launched machines to it, save next changes to a new files in instances, so all new instances are combination of a point to base image and files (anything except of OS) which have the changes. As I learned any VM have .img file consist of OS, data (pics, files, application installed and ...) It means that compute node copy base image to new ephemeral space, boot machine from it and extend it by new change? So base image is only for copy from it and not bind to new instances. Is it correct?

I learned Compute Cache image which received from Glance, Actually I wanted to know more about after caching image in compute node, when launching VM, what happen! 1- Compute node give a copy of image to each new machine, and create .img for them? OR 2- all new machine use one shared base image, so in each VM disk only have just changes with a point to base image? For example I have one image CentOS that as last request cached to compute node, now a user requests 3 new centos VMs, 1-compute node copy 3 times from cached image and give them to new 3 VMs? OR 2- we have one cached common shared image between all 3 VMs? Naturally, if the answer is 2, we save disk space but I should be concerned about losing that shared image and I/O ps. 1 or 2 is correct?

I think we can check the size of new launched VMs, if it is equal or bigger than base image, it shows it have a copy of image in its disk. But unfortunately I do not have access to a VM launched.

Thank you in advance for any help

Image in OpenStack is a shared and common file which binds to all instances or each VM have a copy of that in it's disk?

Hi All

My question is about Image processes that happen when we select Launch machine, I create and upload my base image (ex. CentOS), and want to create an instance from that, Compute node get user request , nova-compute have cached image or ask from glance about image location, get the url of my image, then what happen? It copy base image for new instances? Or because OS in all VMs is repetitious, for saving disk space and …, use base image for number of instance and bind launched machines to it, save next changes to a new files in instances, so all new instances are combination of a point to base image and files (anything except of OS) which have the changes. As I learned any VM have .img file consist of OS, data (pics, files, application installed and ...) It means that compute node copy base image to new ephemeral space, boot machine from it and extend it by new change? So base image is only for copy from it and not bind to new instances. Is it correct?

I learned Compute Cache image which received from Glance, Actually I wanted to know more about after caching image in compute node, when launching VM, what happen! 1- Compute node give a copy of image to each new machine, and create .img for them? OR 2- all new machine use one shared base image, so in each VM disk only have just changes with a point to base image? For example I have one image CentOS that as last request cached to compute node, now a user requests 3 new centos VMs, 1-compute node copy 3 times from cached image and give them to new 3 VMs? OR 2- we have one cached common shared image between all 3 VMs? Naturally, if the answer is 2, we save disk space but I should be concerned about losing that shared image and I/O ps. 1 or 2 is correct?

I think we can check the size of new launched VMs, if it is equal or bigger than base image, it shows it have a copy of image in its disk. But unfortunately I do not have access to a VM launched.

Thank you Thanks in advance for any help