[Users] NFS data domain use host + local storage question

[Jason Keltz]

Hi.

I have a few questions about data domains...

I'm not sure that I understand why when adding a new NFS data domain 
what the "Use Host" is for?

 From the RHEV documentation -  "All communication to the storage domain 
is from the selected host and not directly from the Red Hat Enterprise 
Virtualization Manager. At least one active host must be attached to the 
chosen Data Center before the storage is configured. "

.. but I'm puzzled..  don't all the nodes mount the NFS storage directly 
from the NFS storage server?
Is this saying that if I have two nodes, v1 and v2, and I say "Use Host" 
v1 then v2 gets at storage through v1?  What if v1 is down?
Don't all nodes need a connection to the "logical" storage network?

---

On the topic of local storage...
Right now, I have one node with 1 disk (until some ordered equipment 
arrives)...
/data/images is /dev/mapper/HostVG-Data

I want two of my nodes to store local data.  The majority of VMs will 
use the NFS datastore, but a few VMs need local storage, and I'd like to 
split these VMs across two nodes, so two nodes will have their own local 
storage...

If I was going to install local data on the node, I wouldn't install it 
on the OS disk - I'd want another disk, or maybe even a few disks!    If 
I added another disk to this system, how would I go about making *this* 
disk "/data/images" instead of the root disk? Do I have to reinstall the 
node?

I'm also puzzled by this statement: "A local storage domain can be set 
up on a host. When you set up host to use local storage, the host 
automatically gets added to a new data center and cluster that no other 
hosts can be added to. Multiple host clusters require that all hosts 
have access to all storage domains, which is not possible with local 
storage. Virtual machines created in a single host cluster cannot be 
migrated, fenced or scheduled. "

So .. let's say I have two nodes, both of them have some local disk, and 
use the NFS data store.  I can see why I wouldn't be able to migrate a 
host from one node to the other IF that has was using local data storage 
for the specific virtual machine.  On the other hand, if it's a VM that 
is NOT using local storage, and everything is in the NFS datastore, then 
does this I can't migrate it because each host would have to be in its 
own cluster only because it has local storage for *some* of the VMs!?

Finally - I had previously asked about using MD RAID1 redundancy on the 
root drive, which isn't available yet on the node.  Are there any 
options for creating redundant local storage using MD RAID1, or it's the 
same -- no redundancy on local storage unless you're using a RAID card 
where the driver for that card has been integrated into the node?

Jason.