Re: BHYVE SNAPSHOT image format proposal

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From: Vitaliy Gusev <gusev.vitaliy_at_gmail.com>
Date: Tue, 23 May 2023 17:26:27 UTC

Hi,

> On 23 May 2023, at 19:45, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:
> 
> 
>> 1. BHYVE SNAPSHOT image format:
> 
> Please do not invent Yet Another Format, please ?
> 
> Why not make it a tar(5) file ?
> 

Tar cannot solve issues mentioned in “disadvantages”. Tar doesn’t have versions, it is just container for files
that would introduce another level of indirection. Snapshot/resume doesn’t need just container. It needs
information what is saved and in what format. For example, virtual memory can be saved in different ways: binary,
diff pages, etc.

Virtual memory of VM should be saved faster without additional cost. The same for restore stage. Do you like
an idea to have tar file with size 8 GB ? And how it can be saved efficiently without double copying of data?

Yes, tar is powerful and convenient for many purposes, but it is not so suitable to suspend/resume process and
would introduce just another level of complexity.

——
Vitaliy Gusev