Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1)

[Stefan Hajnoczi]

On Thu, Nov 22, 2012 at 12:12 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Wed, Nov 21, 2012 at 10:01:00AM +0100, Dietmar Maurer wrote:
>> +==Disadvantages==
>> +
>> +* we need to define a new archive format
>> +
>> +Note: Most existing archive formats are optimized to store small files
>> +including file attributes. We simply do not need that for VM archives.
>
> Did you look at the VMDK "Stream-Optimized Compressed" subformat?

We've gone down several sub-threads discussing whether VMDK is
suitable.  I want to summarize why this is a good approach:

The VMDK format already allows for out-of-order data and is supported
by existing tools - this is very important for backups where people
are (rightfully) paranoid about putting their backups in an obscure
format.  They want to be able to access their data years later,
whether your tool is still around or not.

QEMU's implementation has partial support for Stream-Optimized
Compressed images.  If you complete the code for this subformat, not
only does this benefit the VM Backup feature, but it also makes
qemu-img convert more powerful for everyone.  I hope we can kill two
birds with one stone here.

Stefan