Hi,
Let’s say that backup of ovirt engine is done once every day, for example 6 AM 
using engine-backup tool.
Then during the day the changes are made that not only influence the database, 
but actually influence Libvirt/KVM/QEMU
(create/delete VMs,snapshots, disks, ).
Now let’s say at 18:00 an engineer restores from the backup.
How the ovirt will be ‘synchronized’ to Libvirt (/QEMU)?
Of course, it is OK to expect that system is being rolled back, but in that 
scenario there is nothing that I can imagine that will synchronize
Ovirt database state to Libvirt/KVM/QEMU state.
And once anything on (migrate/stop/start) – it will just fail in many cases 
because of inconsistency.
In 4.2 documentation
https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.2/html/self-hosted_engine_guide/reinstalling_hosts_she_backup_restore
there is sentence like:

“If migration is enabled at cluster level, virtual machines are automatically 
migrated to another host in the cluster; as a result, it is recommended that 
host reinstalls are performed at a time when the host’s usage is relatively 
low.“
Let’s say that there are 5 hosts (numbered from 1 to 5), 3 of them are 
hosted-engine (let’s say 1 to 3).
Then first of all, person should find a brand new host (host 6), then install 
HE on that. OK, I understand that HE can be then reinstalled on hosts 1 to 3.
But it when it comes VMs- if really migration of VMs can work, considering 
inconsistency above?
Eg. snapshot that is already in QEMU (done at 11:00) and the volume chain is 
updated is gone from database (because it is restored to 6 AM)
And in general, anything should be done towards non-HE hosts?

So far the restore seems to be very intrusive and quite error-prone in two 
parts: first part is actual handling of VMs.
And second part when ovirt-engine gets configured practically from scratch 
(through that dialog)

BR,
Konstantin

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