[ovirt-users] Questions on oVirt

[jvandewege]

On 3-6-2016 3:23, Brett I. Holcomb wrote:
> After using oVirt for about three months I have some questions that
> really haven't been answered in any of the documentation, posts, or
> found in searching.  Or maybe more correctly I've found some answers
> but am trying to put the pieces I've found together.
>
> My setup is one physical host that used to run VMware ESXi6 and it
> handled running the VMs on an iSCSI LUN on a Synology 3615xs unit.  I
> have one physical Windows workstation and all the servers, DNS, DHCP,
> file, etc. are VMs.  The VMs are on an iSCSI LUN on the Synology.
>
> * Hosted-engine deployment - Run Engine as a VM.  This has the
> advantage of using one machine for host and running the Engine as a VM
> but what are the cons of it?
Not many but I can think of one: if there is a problem with the storage
where the engine VM is running then it can be a challenge to get things
working again. You can guard against that by not using your host as your
main testing workstation :-)

>
> * Can I run the Engine on the host that will run the VMs without
> running it on a VM?  That is I install the OS on my physical box,
> install Engine, then setup datastores (iSCSI LUN), networking etc.
That used to be possible up to 3.5 and is called all-in-one setup.

>
> * How do I run more than one Engine.  With just one there is no
> redundancy so can I run another Engine that access the same
> Datacenter, etc. as the first?  Or does each Engine have to have it's
> own Datacenter and the backup is achieved by migrating between the
> Engine's Datacenters as needed.
There is just one Engine and normally you would have more hosts and it
would migrate around those hosts using the shared storage if you need to
do maintenance on those hosts.

>
> * Given I have a hosted Engine setup how can I "undo" it and  get to
> running just the Engine on the host.  Do I have to undo everything or
> can I just install another instance of the Engine on the host but not
> in a VM, move the VMs to it and then remove the Engine VM.
>
Get a second physical box, install an OS, install Engine on it and
restore the db backup on it and this should work. AIO setup isn't
possible in 3.6 onwards.

> * System shutdown - If I shutdown the host what is the proper
> procedure?  Go to global maintenance mode and then shutdown the host
> or do I have to do some other steps to make sure VMs don't get
> corrupted.  On ESXi we'd put a host into maintenance mode after
> shutting down or moving the VMs so I assume it's the same here.
> Shutdown VMS since there is nowhere to move the VMS, go into global
> maintenance mode. Shutdown.  On startup the  Engine will come up, then
> I start my VMs.
-  Shutdown any VMs that are running
- stop ovirt-ha-agent and ovirt-ha-broker (they keep the Engine up)
- stop the Engine
- stop vdsmd
- stop sanlock
- unmount the shared storage
- shutdown host.
The Engine will come up once you powerup the host. If you use
hosted-engine --set-maintenance --mode=global then ha-agent/ha-broker
won't start the Engine for you. You have to use hosted-engine
--mode=none first. You could add that to your system startup if you
prefer this sequence.
The above is my own recipe and works for me YMMV. (got it scripted and
can post it but it does more or less what I wrote)

>
> * Upgrading engine and host - Do I have to go to maintenance mode then
> run yum to install the new versions on the host and engine and then
> run engine-setup or do I need to go into maintenance mode?  I assume
> the 4.0 production install will be much more involved but hopefully
> keeping updated will make it a little less painful.
>
Its on the wiki somewhere but I think the order is:
- enable global maintenance on the host
- upgrade the engine by running engine-setup and it will tell you
whether it needs a yum upgrade engine-setup or it will do the oVirt
engine upgrade straightaway
- upgrade the rest of the engine packages and restart
- while the engine is down, upgrade the host and restart if needed
-  disable global maintenance on the host and if all is well Engine will
be restarted.

While hosted-engine seems complicated I haven't had any major issues
with it but neither have my other oVirt deployments, standalone Engine
or AIO.

Hope this answers some of your questions,

Joop