[ovirt-users] Questions on oVirt

[Brett I. Holcomb]

On Fri, 2016-06-03 at 03:49 -0300, Charles Tassell wrote:
> Hi Brett,
> 
>    I'm not an expert on oVirt, but from my experience I would say
> you 
> probably want to run the engine as a VM rather than on the bare
> metal.  
> It has a lot of moving parts (PostgresSQL, jBoss, etc...) and they
> all 
> fit well inside the VM.  You can run it right on the bare-metal if
> you 
> want though, as that was the preferred means for versions prior to
> 3.6  
> Also, you don't need to allocate the recommended 16GB of RAM to it
> if 
> you are only running 5-10 VMs.  You can probably get by with a 2-4GB
> VM 
> which makes it more palatable.
> 
>    The thing to realize with oVirt is that the Engine is not the 
> Hypervisor.  The engine is just a management tool.  If it crashes,
> all 
> the VMs continue to run fine without it, so you can just start it
> back 
> up and it will just resume managing everything fine.  If you only
> have 
> one physical host you don't need to really worry too much about 
> redundancy.  I don't think you can assign a host to two engines at
> the 
> same time, but I might be wrong about that.
> 
>    If you want to migrate between a hosted engine and bare metal (or 
> vice versa) you can use the engine-backup command to backup and then 
> restore (same command, different arguments)  the
> configuration.  I've 
> never done it, but it should work fine.
> 
>   For a system shutdown, I would shutdown all of the VMs (do the
> hosted 
> engine last) and then just shutdown the box.  I'm not sure if 
> maintenance mode is actually required or not, so I'd defer to
> someone 
> with more experience.  I know I have done it this way and it doesn't 
> seem to have caused any problems.
> 
>    For upgrades, I'd say shutdown all of the VMs (including the
> hosted 
> engine) then apply your updates, reboot as necessary, and then start
> the 
> VMs back up.  Once everything is up ssh into the hosted engine,
> update 
> it (yum update), reboot as necessary, and you are good to go.  If
> you 
> have a multi-host system that's a bit different.  In that case put a 
> host into maintenance mode; migrate all the VMs to other hosts;
> update 
> it and reboot it; set it as active; migrate the VMs back and move on
> to 
> the next host doing the same thing.  the reason you want to shutdown
> all 
> the VMs is that upgrades to the KVM/qemu packages may crash running
> VMs. 
> I've seen this happen on Ubuntu, so I assume it's the same on
> RedHat/CentOS.
> 
>    As for the 4.0 branch, I'd give it a month or two of being out
> before 
> you use it for a production system.  I started with oVirt just as
> 3.6 
> came out and ran into some bugs that made it quite complicated.  On
> the 
> positive side, I learned a lot about how it works from getting advice
> on 
> how to deal with those issues. :)
> 
> On 2016-06-02 10:23 PM, users-request at ovirt.org wrote:
> > 
> > Message: 4
> > Date: Thu, 02 Jun 2016 21:23:49 -0400
> > From: "Brett I. Holcomb" <biholcomb at l1049h.com>
> > To: users <users at ovirt.org>
> > Subject: [ovirt-users] Questions on oVirt
> > Message-ID: <1464917029.26446.133.camel at l1049h.com>
> > Content-Type: text/plain; charset="utf-8"
> > 
> > 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?
> > 
> > * 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.
> > 
> > * 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.
> > 
> > * 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.
> > 
> > * 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 V
> > Ms.##SELECTION_END##
> > 
> > * 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.
> > 
> > Thanks.
> > 
> > 
Thanks for the input.  That helps.  I spent a lot of time with VMware
and Vcenter so I'm having to readjust some thinking to fit with the
oVirt model.
As for 4.0 I have no intention of trying it until it's released and
been out a while. 
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