Re: [Qemu-devel] [RFC PATCH] drive-backup 'stream' mode

[Eric Blake]

On 10/11/2013 09:18 AM, Wolfgang Richter wrote:
> Idea: Introduce a mode for drive-backup that duplicates writes to
> another target, not CoW.  It is useful for introspecting (my use
> case), and for keeping a remote block device in sync with writes
> (helps with migration or backup).
> 
> 

> 
> This is based off of v1.6.0 code.

Best to rebase it against latest qemu.git.

> +++ b/qapi-schema.json
> @@ -1311,12 +1311,14 @@
>  #
>  # @full: copies data from all images to the destination
>  #
> -# @none: only copy data written from now on
> +# @none: only copy on write data written from now on
> +#
> +# @stream: copy every new write to target

Add the designation '(since 1.7)' to make it obvious when this mode was
introduced.

>  #
>  # Since: 1.3
>  ##
>  { 'enum': 'MirrorSyncMode',
> -  'data': ['top', 'full', 'none'] }
> +  'data': ['top', 'full', 'none', 'stream'] }

MirrorSyncMode is used by multiple commands; your summary mentions how
it would affect 'drive-backup', but what happens to 'drive-mirror'?  For
that matter, why isn't 'drive-mirror' with mode 'none' doing what you
already want?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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