Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present

[Paolo Bonzini]

On 28/09/2015 05:29, Jeff Cody wrote:
> This only occurs under two conditions:
> 
>     1. 'mode' != "existing"
>     2. bdrv_has_zero_init(target) == NULL
> 

I'm not sure if mode != "existing" actually matters.  I think what
actually matters is sync == "full".

The reasons are:

1) with sync != "full", unallocated target sectors should remain
unallocated on the destination because they are supposed to point to the
backing file.

2) even with mode == "existing" you expect the data to be consistent at
the end of the mirroring

Paolo