Re: [Qemu-devel] Live Migration with different block devices

[Xiongzi Ge]

Hi Paolo,

Why the data changed is because the block device is used for a cache device in each host. So, after migration, such block device will be changed, but I still want this vm can access the data in the new block device.  

Thanks

On Tue, Jun 24, 2014 at 4:25 PM, Paolo Bonzini <address@hidden> wrote:

Il 24/06/2014 21:55, Xiongzi Ge ha scritto:

Hi Paolo,

I am trying to do migration with two different block devices in the
source and destination hosts.  For example, in the source the data in
/dev/vda are  'aaaaa'. The guest has a cache. These data are cached.  In
the other host, the data in this device are 'bbbbb'.

Again, what you are doing is invalid.  The point of migration is to have the same thing running on the source and destination, including disk data.

If we do migration, I want the  guest vm recognize this change.

This is not _what_ you want to do.  This is _how_ you want to do it.

(Example: you eat a big mac.  _What_ you want to do is not being hungry.  _How_ you want to do it is going at McDonald's and grabbing a sandwich.  Similar to your migration example, there's probably a better way to achieve your objective).

So, why do you want data to change upon migration?

How does qemu deal with the cache data?  Thanks.

It's not QEMU that's caching data, it's the guest.  There's nothing that QEMU can do about it.

Paolo