Growing qcow2 files during block migration ?

[Christoph Adomeit]

Hi,

I love live migrations using the qemu-kvm block migration Feature (migrate -b) 
but I have a problem with it.

Lets say my source machine has a qcow2 file with virtual size of 60 GB but only 
2 GB are in use. So the qcow2 file only has a size of 2 GB.

After block migration the resulting qcow2 file on the target machine has a size 
of 60 GB.

Also the migration is quite slow because it seems to transfer 60 GB instead of 
2 GB.

Are there any workarounds, ideas/plans to optimize this ?

Thanks
  Christoph
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Re: Growing qcow2 files during block migration ?

[Stefan Hajnoczi]

On Thu, Sep 23, 2010 at 3:40 PM, Christoph Adomeit
christoph.adom...@gatworks.de wrote:
 Lets say my source machine has a qcow2 file with virtual size of 60 GB but 
 only 2 GB are in use. So the qcow2 file only has a size of 2 GB.

 After block migration the resulting qcow2 file on the target machine has a 
 size of 60 GB.

 Also the migration is quite slow because it seems to transfer 60 GB instead 
 of 2 GB.

 Are there any workarounds, ideas/plans to optimize this ?

Yes.  Although this isn't currently possible in mainline QEMU it is
getting attention.  There have been several recent threads on QED,
image streaming, and block migration.  Here is one which touches on
zero sectors:
http://www.spinics.net/linux/fedora/libvir/msg28144.html

Stefan
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