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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 Offline
      olivierlambert Vates 🪐 Co-Founder CEO
      last edited by

      So first, how does "AlmaLinux8-Testing" appear in XO? Like started? If it's the case, you might do a state power reset to it. Then, check the dmesg on the host, I have a feeling there's a connection issue with it.

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      • R Offline
        rustylh @olivierlambert
        last edited by

        @olivierlambert "Failed","Shutting down VM 'AlmaLinux8-Testing' on 'iahost-xcpng-server3'
        Internal error: Object with type VM and id dfcdcce6-b6e1-d865-6f2b-472a35b1fae7/config does not exist in xenopsd","iahost-xcpng-server3","Jun 9, 2025 12:28 PM"

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

          That's why you need to power reset it first.

          Also please check the host dmesg

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          • R Offline
            rustylh @olivierlambert
            last edited by

            @olivierlambert Oh, I'm sorry. You mean power restart the host server?

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            • R Offline
              rustylh @rustylh
              last edited by

              [12:52 iahost-xcpng-server3 ~]# xe vm-reset-powerstate vm=dfcdcce6-b6e1-d865-6f2b-472a35b1fae7 --force
              This operation cannot be completed because the server is still live.
              host: 6985c3a2-091d-488b-8de6-4bf40985987b (iahost-xcpng-server3)

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

                On the pool master:

                1. Restart the toolstack
                2. Immediately after, run the vm reset powerstate command.
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                • R Offline
                  rustylh @olivierlambert
                  last edited by

                  @olivierlambert Ok. I was able to get that VM started on another Host. Now, I need to figure out what is going on with server1. I appreciate all your help! If you have any suggestions please let me know.

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                  • olivierlambertO Offline
                    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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                    • R Offline
                      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 Offline
                        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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                        • R Offline
                          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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                          • R Offline
                            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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                            • R Offline
                              rustylh
                              last edited by

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

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

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

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                                • R Offline
                                  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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                                  • R Offline
                                    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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                                    • R Offline
                                      rustylh
                                      last edited by

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

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                                      • R Offline
                                        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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                                        • R Offline
                                          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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                                          • R Offline
                                            rustylh
                                            last edited by

                                            Any help is greatly appreciated.

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