My Question is not so much in how to do this as i have been able to take an existing Storage domain and increase its size with adding another LUN. My Question is how will a failure of one of the LUNs be handled by the engine and how will it effect the VMs running on it.
Let me setup an example to better illustrate.
Ovirt Node has ISCSI storage domain comprised of 1 Lun from 1 ISCSI based SAN and 2 LUNs from another. So a total of 3 Luns making up the one storage domain.
Now there is an issue with the Storage array providing the single lun. What happens? How do you know what VMs are running on each extent?
It is possible to have LUNs from different storage servers in same storage domain, but it is not recommanded.
The system monitors access to the first LUN in a storage domain every 10 seconds, so truble accesing this LUN will cause this domain to become inactive untill it is accesible again.
Issues with other LUNs may be detected only every 5 minutes, when the system loads LVM metadata from storage.
The system does not consider the allocated extents on LUNs, so it is possible that storage domain will become inactive even if all logical volumes used by running VMs are fine.
For best results using single LUN per domain is best. You can resize the LUN on storage if you need more space.
If you cannot resize LUNs you can add multiple LUNs to a storage domain. For best result don't mix LUNs from multiple servers.
Nir