VM failed and won't start. Displaying "An emulator required to run this VM failed to start"
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@olivierlambert It is full of these:
43342477.643853] sd 7:0:0:1: rejecting I/O to offline device
[43342477.643861] print_req_error: I/O error, dev sdb, sector 0 -
That's exactly what I suspected. You have a connectivity issue with your shared storage.
The device is considered offline because it cannot do any I/O on sector 0
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said in VM failed and won't start. Displaying "An emulator required to run this VM failed to start":
rejecting I/O to offline device
I was able to reboot the host. Now things seam fine. Does that make sense? I mean have you seen this happen then a reboot of the host takes care of it?
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@olivierlambert I had the same issue this morning on one of the hosts I rebooted and was working fine. An emulator required to run this VM Failed to start. sd 7:0:0:1: rejecting I/O to offline device. I am not sure what to check next.
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xcp-ng iscsiadm -m session -P 3 Attached scsi disk sdb State: offline
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There's something fishy about the connectivity to your storage.
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@olivierlambert I am looking into that. I just do not have much experience with the networking.
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I found that the SR has two NICs bonded to two different hardware switches on the iSCSI LUN. Then each host has a management network(Bonded NICS on hosts) and VM network (Bonded NICS). Should I break the SR bond and just go with one NIC? If so, I assume I would be best to shutdown the VMs until I have one NIC on SR reconfigured?
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Additional finding. The two switches (LAG) are Cisco with STP enabled.
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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 -
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
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Any help is greatly appreciated.
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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 deviceright? -
Yes
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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?
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Well, it doesn't happen to every host at the same time, it's just random.
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What log is best to look at for network disconnects?
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Well
dmesgis 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 withdmesg, I would use that to correlate with anything else happening few minutes before. -
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 -
Then try to find anything happening around that time on other hosts, equipment, storage and so on.
