Re: [RFC PATCH 0/2] qemu-img convert: Fix sparseness detection

[Peter Lieven]

> Am 15.04.2021 um 17:22 schrieb Kevin Wolf <kwolf@redhat.com>:
> 
> Peter, three years ago you changed 'qemu-img convert' to sacrifice some
> sparsification in order to get aligned requests on the target image. At
> the time, I thought the impact would be small, but it turns out that
> this can end up wasting gigabytes of storagee (like converting a fully
> zeroed 10 GB image taking 2.8 GB instead of a few kilobytes).
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1882917
> 
> I'm not entirely sure how to attack this best since this is a tradeoff,
> but maybe the approach in this series is still good enough for the case
> that you wanted to fix back then?
> 
> Of course, it would be possible to have a more complete fix like looking
> forward a few blocks more before writing data, but that would probably
> not be entirely trivial because you would have to merge blocks with ZERO
> block status with DATA blocks that contain only zeros. I'm not sure if
> it's worth this complication of the code.

I will try to look into this asap.

Is there a hint which FS I need to set the extent hint when creating the raw 
image? I was not able to do that.

Peter