MDRaid superblock updates

[Kedarius]

Hi all,
Short version of my question: How often and to what extend does mdraid
update superblock on active members? And is there any way how to force
complete update?
Long version:
I have this setup for my virtualization nodes: On an iSCSI server is
physical partition that is exported via iSCSI to all nodes. On the
node where the respective VM is running, this array member is
assembled and started (it can contain more members from more iSCSI
servers, but thats not so important). This md array is used as disk
space for the VM (kvm+qemu+libvirt). This works fine and provides
great degree of flexibility. The only topic I need to solve is live
migration of VMs. I can assemble and start the array on destination
node while it is running on the source node. I have checked that there
is no write operation to the array member till the first write
operation on the array. Qemu guarantees that after the migration is
complete on the source there is a sync on the source and the
destination VM is started after the sync is completed. So this would
work, however I would like to stop the array on the source machine so
the destination node becomes the only one with the array running
again. Unfortunatelly there is no ideal way how to do it via libvirt
or qemu in the right moment. So I am thinking about this scenario:
1) VM running on source with md only on source
2) assemble and run md on destination
3) migrate VM to destination
4) stop the md on source
However step 4 will update array members in the way that the array has
been stoped but the array is running on destination. So now I would
need aditional step 5:
5) on destination force an update of superblocks on the md members to
reflect the actual state (running, etc...)
I came with an idea that for example changing the number of drives in
array (+1,-1) or something like that could force the update I want.