Re: [Qemu-devel] disk image: self-organized format or raw file

[Fam Zheng <famz@redhat.com>]

On Tue, 08/12 08:03, 吴兴博 wrote:
> I carefully read your reply and thought of it carefully. I'm sorry that
> when I said "I get it" I actually meant "I believe you" but not "I
> understand it".
> The problem would not come from cp or rsync -- It's not their fault. They
> just have no way to make it right.
> The real reason of it would be that filesystems have different allocation
> unit size.
> 
> For example, a file is of 16KB in appearance, and the 4KB-12KB of it is a
> hole (0KB-4KB and 12KB-16KB has valid data).
> The FS held it has 4KB block size, so it *could* be allocated like this.
> Copying this file to a filesystem of 16KB block size would cause the entire
> 16KB filled with data, to be specific, the hole is filled with zero and
> cp/rsync have NO way to make difference.
> 
> That's not a engineering issue of cp/rsync. It's a real issue cause by the
> fact that (most) filesystems have configurable block size.
> 

Correct.

It's not an fault of any party, because there is no contract on this part at
all. What you suggested is not a good use case of the file system hole.

Fam