VM failed and won't start. Displaying "An emulator required to run this VM failed to start"

[rustylh]

Additional finding. The two switches (LAG) are Cisco with STP enabled.

[rustylh]

I am still getting " sd 7:0:0:1: rejecting I/O to offline device" taking all VMs on host down. I then shutdown the VM and power them on, on another Host. I have 4 host in a pool connected iSCSI to a Synology LUN. What is the best way to troubleshoot network issues on xcp-ng.
Thank you

[rustylh]

Just adding another note. When I reboot the host everything is fine then the issues pops back up. There doesn't seem to be any consistency as far as timeframe in between. It just happens randomly

[rustylh]

Any help is greatly appreciated.

[olivierlambert]

That's not a trivial problem that you have, it seems to be intermittent and could be anything between host and the storage. I assume you can see the issue as soon you have the rejecting I/O to offline device right?

[rustylh]

Yes

[olivierlambert]

At least we know there's a root cause: the device becomes offline. Could it be a power setting or something on the device itself?

[rustylh]

Well, it doesn't happen to every host at the same time, it's just random.

[rustylh]

What log is best to look at for network disconnects?

[olivierlambert]

Well dmesg is fine, I would also check the switch logs if you have anything happening on the ports where you host are connected. Since you can find when it's happening with dmesg, I would use that to correlate with anything else happening few minutes before.

[rustylh]

dmesg -T is only showing these from 00:37 on.

[Mon Jun 30 05:55:10 2025] print_req_error: I/O error, dev sdb, sector 0
[Mon Jun 30 05:55:10 2025] sd 7:0:0:1: rejecting I/O to offline device

[olivierlambert]

Then try to find anything happening around that time on other hosts, equipment, storage and so on.