@john-c
Would you mind to post your custom.conf so i have a reference?

@john-c
As i mentioned i am not a pro in regard of iscsi and multipath.conf. If you are, can you just look over the settings and give your opinion on it?

And do i just put this into the custom.conf:

        device {
                vendor                  "TrueNAS"
                product                 "iSCSI"
                path_selector           "round-robin 0"
                path_grouping_policy    multibus
                hardware_handler        "0"
                prio                    "const"
                failback                immediate
        }

without the outer devices {}

@john-c
Thanks for this information. I will put it into the custom.conf

I had a similar problem with a TrueNAS Server. On the host multipath was enabled and connecting to Synology iSCSI target was not a problem at all. Connecting to the TrueNAS target was not working with an error:

sr.probeIscsiExists
{
  "host": "81e4f97f-bc48-4b11-9ece-97f395c7e24c",
  "target": "172.16.1.21",
  "targetIqn": "iqn.2024-11.com.truenas:target0",
  "scsiId": "36589cfc0000000de53d4a06991332938",
  "port": 3260
}
{
  "code": "SR_BACKEND_FAILURE_432",
  "params": [
    "",
    "Device Mapper path missing [opterr=Device mapper path /dev/mapper/36589cfc0000000de53d4a06991332938 not found]",
    ""
  ],
  "call": {
    "duration": 10810,
    "method": "SR.probe",
    "params": [
      "OpaqueRef:1cdb7e37-eb90-4644-8ac1-37fddfd7e58c",
      {
        "target": "172.16.1.21",
        "targetIQN": "iqn.2024-11.com.truenas:target0",
        "SCSIid": "36589cfc0000000de53d4a06991332938",
        "port": "3260"
      },
      "lvmoiscsi",
      {}
    ]
  },
  "message": "SR_BACKEND_FAILURE_432(, Device Mapper path missing [opterr=Device mapper path /dev/mapper/36589cfc0000000de53d4a06991332938 not found], )",
  "name": "XapiError",
  "stack": "XapiError: SR_BACKEND_FAILURE_432(, Device Mapper path missing [opterr=Device mapper path /dev/mapper/36589cfc0000000de53d4a06991332938 not found], )
    at Function.wrap (file:///opt/xo/xo-builds/xen-orchestra-202411020002/packages/xen-api/_XapiError.mjs:16:12)
    at file:///opt/xo/xo-builds/xen-orchestra-202411020002/packages/xen-api/transports/json-rpc.mjs:38:21
    at runNextTicks (node:internal/process/task_queues:60:5)
    at processImmediate (node:internal/timers:454:9)
    at process.callbackTrampoline (node:internal/async_hooks:130:17)"
}

After researching 2 days and working with chatgpt the solution was to change /etc/multipath.conf. At the end of the file there was a section with an device for TrueNAS.
I changed it to:

        device {
                vendor                  "TrueNAS"
                product                 "iSCSI"
                path_selector           "round-robin 0"
                path_grouping_policy    multibus
                hardware_handler        "0"
                prio                    "const"
                failback                immediate
        }

I am not an expert on the configured settings. It was what chatgpt suggested. So maybe if someone can view this settings and maybe we can then add it to the standard configuration which comes with XCP-ng. Maybe @olivierlambert can view this and we can put it on github.

Does the /etc/multipath/conf.d/custom.conf override the existing device configuration in /etc/multipath.conf?