Re: [Qemu-devel] VHD suport in QEMU?

[Jeff Cody]

On Fri, Nov 01, 2013 at 06:04:19AM +0100, Philipp Hahn wrote:
> Hello,
> 
> sorry for high-jacking this thread, but I have a questing regarding VHD 
> (without the X): Xen-4.3 switched to upstream QEMUs support for VHD. The 
> dropped their own VHD implementation in blktap2, which supported backing 
> chains, which QEMU currently doesn't. The Xen implementation 
> (xen/tools/blktap2/vhd/lib/ is BSD 3 clause) also supports some kind of 
> journal.
> 1. Does someone know if the journal support for VHD is somehow related to 
> VHDX?

I don't believe it is.  Despite the similarity in names, VHD and VHDX
are completely different formats.

I just went and looked at Xen's libvhd-journal, and per my
understanding it is a journal written into a separate file, not
related to the actual VHD spec itself.

It appears to be used by the VHD utility tools, when updating a VHD
image file with operations such as resize, etc.., so they can write a
finalized bitmap of all header/metadata changes at once to minimize
any potential corruption.

Jeff

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