Re: [ovirt-users] Questions on oVirt

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(a)ovirt.org wrote: > > Message: 4 > Date: Thu, 02 Jun 2016 21:23:49 -0400 > From: "Brett I. Holcomb" <biholcomb(a)l1049h.com&gt; > To: users <users(a)ovirt.org&gt; > Subject: [ovirt-users] Questions on oVirt > Message-ID: <1464917029.26446.133.camel(a)l1049h.com&gt; > 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. > >