I just added a few LUN's to our new EMC VNX, and the LUN ID's are not consistent..
Screenshot from EMC Unisphere
Screenshot from VMWare vSphere
If you study the two screenshots carefully, you'll notice that the Unique ID is identical, yet the LUN ID's differ. I'm a bit at a halt here, and I'm not sure if I should call EMC and blame them, or start searching the net for potential vSphere bugs..
Ok - I'm adding this in case of anyone else gets the same problem. It's a bit embarrassing that I didn't check this first.. :-)
EMC VNX (Clariion) uses a concept of Storage Groups to map LUN's to hosts. For some reason, you have to select what the Host ID LUN should be when you map it. One possible scenario could be sharing a LUN between several servers, where one of the LUN's could already be in use on one of the hosts.
Example:
It helped when I was adding a LUN on our VNX and my VMware hosts were getting a different host ID number.
The only way for you to choose the HOST ID number is:
On the Selected LUN list, found the recently added LUN and click on the Dropp Down menu on the Host LUN ID collumn;
PS: The LUN cannot belong to any Storage Groups in order for you to change the host id number.