[CRIU] CRIU Queries Live Migration V/S Disk-less Migration

[Pavel Emelyanov]

On 10/15/2015 06:53 PM, Prashant Chillabatte wrote:
> 
> Hello All,
> 
> I started using criu from few days back. I have few quires after using CRIU for few weeks.
> 
> I would really appreciate your helping hands on understanding CRIU better.
> 
> 1st Query:
> I failed to understand the difference between the live migration and disk-less migration.
> 
>    In live migration
> 
> ●Take the snapshot of the process
> ●Copy them into some shared folders.[involves creating images files of both memory and context and pasting/dumping at a directory ]
> 
>    In disk-less migration
> 
> ●Take the snapshot of the process
> ●Transfer the process memory related files[Transfer involves creating memory image files and pasting/dumping them on the restore side ] ->> this step looks like same as coping into shared folder in live migration
> ●Copy process context image files using scp.
> 
>    I fail to understand the difference, can someone give a better understanding of the same.

When you just live migrate a container you should keep images with memory contents
on source node FS, then copy them to the destination one. In disk-less live migration
you can send memory dumps directly to the destination host using page server.

> 2nd Query:
> I want to know about page-server, what does page-server do?How different it is from secure copying like scp.

The main advantage when using page server is that you don't have to keep memory dumps
in two places -- source node and destination one.

> 3rd Query:
> What does live migration exactly means?
> My understanding after using CRIU for few weeks:
> ■Process running on node 1
> ■Checkpointthe process
> ■Restore the process on the 2nd node
> 
> And the process/application/service under migration has downtime equivalent to time elapsed between checkpoint and restore.
> 
> Correct me if i am wrong.
> 
> Thanks,
> Prashanth Chillabatte
> 
> 
> 
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