Re: [Qemu-devel] qemu drive-mirror to rbd storage : no sparse rbd image

[Fam Zheng]

On Sat, 10/11 10:00, Alexandre DERUMIER wrote:
> >>What is the source format? If the zero clusters are actually unallocated in 
> >>the
> >>source image, drive-mirror will not write those clusters either. I.e. with
> >>"drive-mirror sync=top", both source and target should have the same 
> >>"qemu-img
> >>map" output.
> 
> Thanks for your reply,
> 
> I had tried drive mirror (sync=full) with
> 
> raw file (sparse) -> rbd  (no sparse)
> rbd (sparse) -> rbd (no sparse)
> raw file (sparse) -> qcow2 on ext4  (sparse)
> rbd (sparse) -> raw on ext4 (sparse)
> 
> Also I see that I have the same problem with target file format on xfs.
> 
> raw file (sparse) -> qcow2 on xfs  (no sparse)
> rbd (sparse) -> raw on xfs (no sparse)
> 

These don't tell me much. Maybe it's better to show the actual commands and how
you tell sparse from no sparse?

Does "qcow2 -> qcow2" work for you on xfs?

> 
> I only have this problem with drive-mirror, qemu-img convert seem to simply 
> skip zero blocks.
> 
> 
> Or maybe this is because I'm using sync=full ?
> 
> What is the difference between full and top ?
> 
> ""sync": what parts of the disk image should be copied to the destination;
>   possibilities include "full" for all the disk, "top" for only the sectors
>   allocated in the topmost image".
> 
> (what is topmost image ?)

For "sync=top", only the clusters allocated in the image itself is copied; for
"full", all those clusters allocated in the image itself, and its backing
image, and it's backing's backing image, ..., are copied.

The image itself, having a backing image or not, is called the topmost image.

Fam