CBT: the thread to centralize your feedback

StormMaster

@olivierlambert @florent If it helps to know... Disabling "Use NBD + CBT to transfer disk if available" on the same backup jobs as I used above works flawlessly. Although on big backup jobs, not having NBD available does add about a quarter of the time to the backup process.

rtjdamen

@StormMaster i understand, we are also not using this on these vms but it does make sense, something is breaking the cbt chain and causing a full, question is if this is caused by the backup job or something else. Thanks for your input.

andyh

I was looking to do some updates on our TrueNAS Scale device providing an NFS share to my XCP-ng hosts (8.2.1), we have CBT enabled for backups.

However when I try to move the Xen Orchestra VDI from TrueNAS to local storage I receive the following error:

{
  "id": "0m261vorl",
  "properties": {
    "method": "vdi.migrate",
    "params": {
      "id": "f91f81f2-308d-4de9-879e-c1fa84a37d27",
      "sr_id": "49822b62-3367-7e7c-76ee-1cfc91a262e9"
    },
    "name": "API call: vdi.migrate",
    "userId": "7b63bade-51f3-4916-9174-f969da17774a",
    "type": "api.call"
  },
  "start": 1728731129889,
  "status": "failure",
  "updatedAt": 1728731132752,
  "end": 1728731132752,
  "result": {
    "code": "VDI_CBT_ENABLED",
    "params": [
      "OpaqueRef:4f16cd0e-fbaf-48c3-aae4-092b9906b9e4"
    ],
    "task": {
      "uuid": "7ce61fba-d6d3-12cb-2585-79d5b69d3857",
      "name_label": "Async.VDI.pool_migrate",
      "name_description": "",
      "allowed_operations": [],
      "current_operations": {},
      "created": "20241012T11:05:31Z",
      "finished": "20241012T11:05:32Z",
      "status": "failure",
      "resident_on": "OpaqueRef:fe0440a3-4a31-44d6-8317-a0e64d0ee01e",
      "progress": 1,
      "type": "<none/>",
      "result": "",
      "error_info": [
        "VDI_CBT_ENABLED",
        "OpaqueRef:4f16cd0e-fbaf-48c3-aae4-092b9906b9e4"
      ],
      "other_config": {},
      "subtask_of": "OpaqueRef:NULL",
      "subtasks": [],
      "backtrace": "(((process xapi)(filename ocaml/xapi-client/client.ml)(line 7))((process xapi)(filename ocaml/xapi-client/client.ml)(line 19))((process xapi)(filename ocaml/xapi-client/client.ml)(line 12359))((process xapi)(filename lib/xapi-stdext-pervasives/pervasiveext.ml)(line 24))((process xapi)(filename lib/xapi-stdext-pervasives/pervasiveext.ml)(line 35))((process xapi)(filename ocaml/xapi/message_forwarding.ml)(line 134))((process xapi)(filename lib/xapi-stdext-pervasives/pervasiveext.ml)(line 24))((process xapi)(filename lib/xapi-stdext-pervasives/pervasiveext.ml)(line 35))((process xapi)(filename lib/xapi-stdext-pervasives/pervasiveext.ml)(line 24))((process xapi)(filename ocaml/xapi/rbac.ml)(line 205))((process xapi)(filename ocaml/xapi/server_helpers.ml)(line 95)))"
    },
    "message": "VDI_CBT_ENABLED(OpaqueRef:4f16cd0e-fbaf-48c3-aae4-092b9906b9e4)",
    "name": "XapiError",
    "stack": "XapiError: VDI_CBT_ENABLED(OpaqueRef:4f16cd0e-fbaf-48c3-aae4-092b9906b9e4)\n    at Function.wrap (file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/_XapiError.mjs:16:12)\n    at default (file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/_getTaskResult.mjs:13:29)\n    at Xapi._addRecordToCache (file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/index.mjs:1041:24)\n    at file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/index.mjs:1075:14\n    at Array.forEach (<anonymous>)\n    at Xapi._processEvents (file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/index.mjs:1065:12)\n    at Xapi._watchEvents (file:///opt/xo/xo-builds/xen-orchestra-202410111017/packages/xen-api/index.mjs:1238:14)"
  }
}

I can see a task disabling CBT on the disk and looking at the UI it shows as CBT disabled.

I experience the same issue attempting to migrate other VDI's too.

rtjdamen

You need to remove all snapshots before migration and disable cbt. Storage migration is not supported when cbt is invalid. I believe xoa should do this automatically however.

andyh

@rtjdamen Thanks for the super fast response!

Just removed the existing snapshots and the task is proceeding.

Did you mean cbt is enabled as opposed to cbt is invalid?

rtjdamen

@andyh no cbt should be disabled, u can’t migrate an cbt enabled vdi.

andyh

@rtjdamen I understand now

flakpyro

After a number of XOA Updates i decided to test CBT with snapshot delete again.

Instead of " "can't create a stream from a metadata VDI, fall back to a base" i am seeing a more verbose error but the issue remains the same. In a 2 host pool with shared NFS storage if i have CBT with Snap delete enabled after a VM is migrated from host A to host B (remaining on the shared NFS SR) and a backup runs the delta backup fails and a full runs. This time the error shows " Can't do delta with this vdi, transfer will be a full"

This is with XOA Latest: 5.100.0

I have attached the backup log if this helps.

2024-11-05T17_37_58.455Z - backup NG.json.txt

rtjdamen

@flakpyro in general this error means that the cbt is not valid, we have seen this as well and i know vates is looking into this. In general we saw this problem more on nfs then on iscsi, not shure if it is nfs related but maybe if u have access to an iscsi target try your results there.

flakpyro

@rtjdamen this test pool is running on TrueNAS, so i could configure iSCSI. Our production is on NFS so i tried to keep test close to the same as far as storage is concerned. We currently use NBD + CBT without the snapshot delete function in production and it works well via NFS. Will continue to keep testing as updates roll out and look forward to when this is completely stable. If there's anything anyone at Vates needs log or test wise i'm happy to help!

rtjdamen

@flakpyro i think that would be a good test, can u check how it is behaving on iscsi on your end?