On Thu, 2013-07-25 at 09:55 -0400, Jason Keltz wrote: > On 07/25/2013 09:27 AM, René Koch (ovido) wrote: > > On Thu, 2013-07-25 at 09:07 -0400, Jason Keltz wrote: > >> 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? > > > > Hi, > > > > You need a host to initialize the storage. > > The host you have to choose with "Use Host" initially creates the data > > structure,... on the storage. > > > > Afterwards all host in your cluster will mount the storage and write > > data for their vms. There's no one-node bottleneck. > > > Great! Got it .. thanks.. > > >> --- > >> > >> 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... > > > > So you will have vm storage on node01, node02 and on your NFS storage, > > right? > > > > All the VMs on node01 and node02 would be stored on the NFS datastore. > Most of the VMs would have any required data stored on the NFS datastore > as well. > A few of the VMs on node01 and node02 would have a requirement for a > local data store. > > >> 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 would recommend to use LVM and add new disks into your logical > > volume... > If I added another disk, would I be able to remove the existing > datastore through the engine, and create a new one pointing at only the > new disk?
Afaik if you add another local data store the existing one will become inaccessible from within oVirt. If I remember correctly a new datacenter and new storage domain will be created and the original one will be dropped from oVirt, but still contains data. > >> 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!? > > > > Each local storage host requires it's own datacenter and you can't mix a > > datacenter with local storage with NFS storage. > sigh. This seems so rigid! I understand, for example, why clusters > must encompass same CPU type. I do not understand why a host cannot > connect to both local data storage, and NFS storage. > > > What I would do in your case: > > 1. Use CentOS/Fedora hosts instead of oVirt-Node. > > 2. Configure NFS-Server on each Node. > > 3. Have 1 datacenter with 1 cluster and 2 nodes with storage type NFS. > > 4. Add 3 storage data domains (NFS-Share of each host and NFS-Share of > > your main NFS server). > > 5. Bind vms with local NFS server to local host... > I never thought of that... very interesting! I was really trying not > to use anything but oVirt node to keep the implementation as simple as > possible. The only problem here if I understand correctly is that each > node is still accessing even its local data via NFS, in which case, they > might as well be storing the data on the NFS server itself! :) Yes, in this scenario a node accesses its local data via its local NFS server. I have this setup in production on customer side where nodes have a lot of disk space and I/O isn't a criteria. I personally always configure local NFS servers instead of local storage as I have better experience with it (had some issues with local storage). I also prefer a CentOS/Fedora host over oVirt-node as it's easier to manually configure network (this is sometimes needed) or troubleshoot / install monitoring and backup tools or kernel modules for specifiy network adapters,... as on oVirt node. Others may prefer oVirt node due to easy update possibility :) > > Or with GlusterFS: > > 1. Use CentOS/Fedora hosts instead of oVirt-Node. > > 2. Configure replicated GlusterFS volume over your 2 nodes > > 3. Have 1 datacenter with 1 cluster and 2 nodes with storage type NFS > > 4. Add 2 storage data domains (NFS-Share of GlusterFS volume and > > NFS-Share of your main NFS server). > > > > Disadvantage of GlusterFS with NFS: one of your 2 nodes is exporting the > > NFS share and if this node is down your storage domain is down and you > > have to manually fix the mount. > Agreed. > >> 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? > > > > MD-Raid or DRBD,... isn't possible, (yet?). > > You could try GlusterFS 3.4 (replicated volume over your 2 nodes)... > > > > Hope this helps. > Thanks very much for your useful feedback. You're welcome. > > Jason. > _______________________________________________ Users mailing list [email protected] http://lists.ovirt.org/mailman/listinfo/users
