On Fri, Dec 23, 2016 at 5:10 PM, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:
Hello,
in June 2016 oVirt 4.0.0 GA was released and I in-place upgraded from an existing 3.6.5 to it.
In 4.0.0 release notes it was described as the method to use.
I see that it still remains the same for 4.0.5:
and also for upcoming 4.0.6 (RC5 at least) there is not yet anything special:

Instead, if I go and read the RHEV 4.0 documentation I notice:

"
Red Hat Virtualization Manager 4.0 is only supported on Red Hat Enterprise Linux 7. A clean installation of Red Hat Enterprise Linux 7 and Red Hat Virtualization Manager 4.0 is required, even if you are using the same physical machine used to run Red Hat Enterprise Virtualization Manager 3.6. The upgrade process involves restoring Red Hat Enterprise Virtualization Manager 3.6 backup files onto the Red Hat Virtualization Manager 4.0 machine.
"

Is there any particular technical reason for this substantial difference?

Ciao Gianluca,
the point is that RHEV-M 3.6 has never been released for RHEL7 but just for RHEL6 while RHV-M 4.0 is available only for RHEL7 so you have for sure to replace your OS before installing RHV-M and so the backup/restore procedure.
Upstream it's different because oVirt engine 3.6 was already available on el7 so, just in that case, you can simple upgrade in place.

Clearly they are not the same sw but it seems strange to me this discrepancy.

Suppose I have a mix of oVirt and RHEV environments it could be simpler to have a common path, where possible.

For example, can I also use the documented RHEV approach for oVirt? At what extent?

The in-place upgrade is a lot simpler and fast and so definitively recommended if available but technically nothing is preventing you from upgrading from oVirt engine 3.6 to oVirt engine 4.0 reinstalling the OS and restoring a backup there.
A tool to migrate an hosted-engine env from a VM with 3.6/el6 to 4.0/el7 is also available:
https://www.ovirt.org/develop/release-management/features/hosted-engine-migration-to-4-0/
Also in that case, if you are already on el7, it's by far easier to simply upgrade in place.
 

Thanks
Gianluca 

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