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

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    • olivierlambertO Online
      olivierlambert Vates 🪐 Co-Founder CEO
      last edited by

      My suggestion stands from previous messages, check the dmesg output from the problematic host 🙂

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        rustylh @olivierlambert
        last edited by

        @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

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        • olivierlambertO Online
          olivierlambert Vates 🪐 Co-Founder CEO
          last edited by

          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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            rustylh
            last edited by

            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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              rustylh @olivierlambert
              last edited by

              @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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                rustylh
                last edited by

                xcp-ng iscsiadm -m session -P 3 Attached scsi disk sdb State: offline

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                • olivierlambertO Online
                  olivierlambert Vates 🪐 Co-Founder CEO
                  last edited by

                  There's something fishy about the connectivity to your storage.

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                    rustylh @olivierlambert
                    last edited by

                    @olivierlambert I am looking into that. I just do not have much experience with the networking.

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                      rustylh
                      last edited by

                      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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                        rustylh
                        last edited by

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

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                          rustylh
                          last edited by

                          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

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                            rustylh
                            last edited by

                            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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                              rustylh
                              last edited by

                              Any help is greatly appreciated.

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                              • olivierlambertO Online
                                olivierlambert Vates 🪐 Co-Founder CEO
                                last edited by

                                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?

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                                  rustylh
                                  last edited by

                                  Yes

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                                  • olivierlambertO Online
                                    olivierlambert Vates 🪐 Co-Founder CEO
                                    last edited by

                                    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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                                      rustylh
                                      last edited by

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

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                                        rustylh
                                        last edited by

                                        What log is best to look at for network disconnects?

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                                        • olivierlambertO Online
                                          olivierlambert Vates 🪐 Co-Founder CEO
                                          last edited by

                                          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.

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                                            rustylh
                                            last edited by

                                            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

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