The problem has solved itself. XCP-ng installer can't even be run on my PC (with UEFI). Some core-dump pops up and resets. For a test, I tried the installation on an old but problem-free laptop (in BIOS mode). Installation without a problem, but does not boot (OS not found).
I have to look for another hypervisor. If the installer is already causing problems, then I don't want to know what to expect next.
So the topic can be closed and even deleted.

@rtjdamen said in Migration over NAS and slow connection.:

Its not possible to upgrade vmware to xcp-ng with the vms on it.

That's quite understandable

I don't have a second real server either. I spent $200 on RAM and SSDs to bring my 8-core home PC up to the hypervisor requirements for 4 VMs. That should be enough to tide me over for a week or two, if the real server fails, before I fix it or buy a new one.

I'm not going to move completely right away because I'm not familiar with XCP-ng. It would be too dangerous for business, aside from the downtime (it would be doable on Sunday). I want to look at XCP first and test it for some time.
Hence the idea of doing it via NAS.

But I don't reject the option of deleting the vmware and installing XCP-ng if it works well on the backup server. That is actually the goal. First learn with backup-server, then move completely.

@rtjdamen Hi,
thanks for quick reply, however how can I install XCP-ng on the host in office if it's running ESXi? As a VM? I thought XCP-ng is type 1 hypervisor...

Hello everyone.

Before I switch completely to XCP-ng, I want to play with it a bit and set up an ad-hoc backup server at the same time.

What I have:
There are two locations: office and home.
Office: A server with ESXi-7 (4 VMs, 500GB, no vCenter) and a Synology DS220j - both running 24/7.
At home: Synology DS220j (runs 24/7, daily backup from office: documents, databases) and a somewhat lavish PC, which is to act as an emergency server. XCP-ng should be installed on it but not run permanently, only if the server in the office breaks down.
Locations are permanently connected with IPSec (relatively slow, approx. 20Mbit upload from the office). I know - sending 500GB over 20Mbit takes 2.5 days. Maybe for first “rsync” FloppyNet can be considered (or nowadays: USB disk).

What I would like to have:
My thoughts are to often do a VMs export from ESXi to the office NAS. Once a week (or month, or after major update in VMs) a rsync (or over FloppyNet if no incremental doable) to NAS at home. So I will have the VMs in 1Gbit network. From time to time import the VM into XCP at home, maybe update XCP itself.
In case of disaster: start oversized PC with XCP-ng, import VMs from home NAS, customize networks in VMs and start/connect. In the worst case, an hour or two of downtime.
If it happens shortly after update - few minutes (only import DBs).

Is it possible? If yes, how?
Greets, Tadek
PS. Sorry for my AI-English