I managed to successfully do the migration of the iscsi storage domain for my 
hosted engine, from one host/target to another.
For posterity, here's how it went for me, skipping a few failed attempts.
Sorry for formatting

Note #1: oVirt 4.3, using the ovirt supplied "node" images for hosts

Note #2: this takes a really.. REALLY.. long time.  over an hour. possibly 
closer to 2 hours.

My Steps:

*. make sure that the hosted_engine vm is NOT running on node #1 of my cluster, 
so I have a fallback if I need it

*. do a "engine-backup" from the hosted_engine vm command line, and scp the 
resulting 7mb file out to node #1 of my cluster

*. create a new iscsi LUN for a new hosted_engine storage domain

*. put the cluster in global maint, with
    hosted-engine  --set-maintenance --mode=global

*. shut down the hosted engine VM

*. on node #1, do   

*. on node #1, 
    systemctl enable firewalld; systemctl start firewalld

   and then doublecheck that
    firewalld --list-services

   showed all the good things, including ssh and cockpit

*. on node #1, 

   *** note: NOT engine-backup --mode=restore after the fact.
        I'm glad I happened to stumble on this feature. I think.

*. Press return a lot. Occasionally actually putting in specifics of things.

  - Side quest: Since I had no idea how I was supposed to set up the new iSCSI 
storage domain, I chose the option for

         .... Pause the execution after adding this host to the engine?
          You will be able to iteratively connect to the restored engine.. 

    Turns out, this was NOT needed. but I got to learn a few things. such as, 
the install process RENAMES any existing
    storage domain called "hosted_storage" to "hosted_storage_old_xxxxxx"
     So, this may have a "point of no return" point

*. Wait. 
    A LOT
      output said something about wait until VM gets into run state. or maybe 
it was
       TASK [ovirt.engine-setup : Make sure `ovirt-engine` service is running]
    This took something like 10 minute or more, while giving ZERO feedback to 
    I wondered if it had locked up or somthing, and was tempted to kill it, but 
instead, I eventually left for lunch.
    Good thing.

*. notice that the process creates a TEMPORARY "external engine" VM.. that is 
maybe stored on host local disks or something? I dont know details. 
    but this is what allowed me to connect in via browser and check out how 
things looked, when it prompted me that I could.

*. When I was ready, remove the trigger file /tmp/somethingsomething (via a 
separate window ssh session)

*. Answer a bunch more text prompts about what iSCSI host I want to connect to, 
and then which target to use, and then which lun.
   Finally, it got around to creating the new storage domain for hosted engine, 
on the new LUN.

  *** Fun fact ***. It just gives you lun sizes. It does not give you ACTUAL 
lun numbers for the target you select to use.
    Specifically, it showed me my "lun #2" as MENU CHOICE #1.
    So make sure you make all your luns slightly different sizes!
    Also, it has NO AWARENESS of EXISTING STORAGE DOMAINS. In fact, it silently 
overwrote a new storage domain I had called "hosted_storage",
    after I noticed that the prior one had been renamed

*. Wait
    A long. time.

I am happy to say that eventually, it actually finished up what it was doing.
It then informed me that I had to go to each of the other hosts (through the 
hosted engine GUI) and individually
    1. put the host in maintenance mode
    2. choose  Installation  -> Reinstall
        AND manually reenable the Hosted engine install, for those hosts that I 
want it on again.

I am happy to report that this went smoothly.

Here ends my tale  :)


----- Original Message -----
From: "Philip Brown" <pbr...@medata.com>
To: "Alan" <alan+ov...@griff.me.uk>
Cc: "users" <users@ovirt.org>
Sent: Monday, July 27, 2020 11:39:39 AM
Subject: Re: [ovirt-users] change lun for hosted_engine use?

To someone who has never dealt with the backup/restore stuff.. not to mention 
taking over a previously setup cluster.. it is exceedingly onerous :(

Those docs seem geared primarily towards doing backup and restore of a 
hosted_engine where nothing is changing.
it would be really helpful to have docs where the goal is changing the 
environment for the hosted engine.
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