[Users] NFS data domain use host + local storage question
Jason Keltz
jas at cse.yorku.ca
Thu Jul 25 13:07:28 UTC 2013
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.
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