8:50 p.m.
On Friday, August 18, 2017 1:20:23 PM EDT Mitchell Smith wrote:
Hi List,
I am in the process of deploying ovirt in a lab environment before
implementing it in production.
My lab consists of three compute hosts and one engine host.
I am using the 4.2 nightly builds in this lab environment, mainly because I
want to test the OVN functionality.
I wanted to add a NFS data domain on the engine host to store VM templates
and ISO images, however when I go in to Storage -> Domains -> New and try
and add a NFS domain, it only gives me the three compute hosts to create
storage on, I’m guessing because the engine host doesn’t have VDSM
installed.
Is there a way to do this, so I can make use of the considerable free space
on the engine host, or do I have to add it as a compute host running VDSM,
and if so how can I flag this host so no VMs get deployed on it, I only
want to use the storage capacity.
Any feedback or suggestions would be very much appreciated.
Thanks in advance.
Mitch
I think you are misunderstanding the architecture of oVirt a little bit so I
will try to explain, and then I will address your particular issue. Basically
the following happens:
1. The engine talks to the hosts (which are running VDSM). The engine itself
doesn't actually know about or care about the storage at all, it just talks to
the hosts. If storage operations need to happen it tells a special host, the
SPM to do them. Only one host at a time is SPM.
2. The hosts talk to the storage through whatever mechanism is provided by the
storage (FC, iSCSI, NFS, Gluster, etc). Management of the storage happens
through the SPM host (this is to prevent simultanious operations that could
corrupt the storage). This also means that under normal circumstances the
available disk space on the hosts is not used (unless you are running some
kind of hyper converged setup, which is a whole other story). Of course a lot
of this is a little more nuanced than what I am saying, but in general the
storage is considered separate from the hosts.
When you add a host to the engine you are simply saying this machine is
available to RUN VMs and it should be able to communicate with the storage
domains. Which leads to your question about why are you not seeing the storage
available on the engine machine. In the NFS dialog you have to specify a HOST
to use to connect to your storage (Not sure why, since I figured the SPM would
be a good default, but you should ask the storage guys). Anyway I guess the
host you pick will be the one that does the checks and mounts the NFS share
and creates the storage domain on the NFS.
Now in your case you should create the NFS share on the engine machine, make
sure it is visible to all your hosts, and pick one host from the list to
connect to that share and configure the domain on it (You will have to specify
the mount/etc). So at that point the machine with the engine, will be the
engine machine AND the storage.
Now this is not a really good idea for production as when that machine goes
down, you will have lost both your engine and your storage at the same time.
Causing your VMs to pause, and you lost your ability to manage the environment
because the engine is down.
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