[ovirt-users] Questions on oVirt

Fri Jun 3 16:10:41 UTC 2016

On Fri, 2016-06-03 at 08:41 +0200, jvandewege wrote:
> 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 :-)
Unfortunately, I only have one physical host available.  The storage is
NFS on the host which has a RAID10 array setup.  Not optimum but it's
what I've got.
> > 
> > 
> > * 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.
> 

I remember reading about that and it's deprecated if I remember.
> > 
> > 
> > * 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)
> 
> 

Thanks.  That helps.  If you get a chance I'd like the script.
> > 
> > 
> > * 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
> 
> 
> 

Thanks.  This clarifies a lot.  I had things down pat with ESXi but
with oVirt I have to learn how it thinks.
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