The problem I see is that there are 8 volumes in the NetApp, 5 on one aggregate, 3 on another. There are 6 volumes presented and used in XenCenter for storage. So there are two volumes missing from XenCenter. One of the ones I can't see has the word "root" in its name, and is only 1GB in size, so I wouldn't expect that to be showing. The other one I can't see in XenCenter is showing in the NetApp OnCommand System Manager as 1 TB and unused, so I am puzzled as to why it's not in XenCenter like the others.
I guess it just hasn't been added, for some reason. I have inherited this system. I now know that we have support, so I'll ask them. Meanwhile it's been helpful just to "talk it out".
To answer your questions:
1. I don't know, what is OnTap?!
2. FC, same as the others. Yes the service is up. We also have an older NetApp connected which uses iSCSI, that's working OK.
3. I believe there is a LUN inside the volume.
4 & 5, now you've lost me, I am not familiar with igroup, and can't see that in the NetApp OnCommand System Manager.
6. No, that's the problem.
Thanks for your help, and your helpful links. The first link is broken, by the way.