@stormi ok, so "Install pool patches" and "Rolling pool update" internally behave completely different. This is new for me, until now, i thought, the Rolling Pool Update is a "Install poool patches" with following evacuation and reboot of the nodes, so thats what I have done manually today. Thanks for the explanation ...

@stormi I alwas used the rolling pool update since its available so i did not read the docs since then any more. If I understand you correct, until now the rolling pool update does not do a toolstack restart during the node restarts although it is so important?

@stormi I read the warning about problems with the rolling-pool-update, so after updating the pool with xen-orchestra, i wanted to live-migrate the Vms manually with xen-center. But live-migration fails, an the VMs crashed. I had to stop the other vms on the master and then reboot to get them back online.
After that I shut down the other VMs to savely reboot the other nodes.

So I think, the warning is not fully correct, also without using the rolling-pool-update feature you can get into trouble. Maybe the mentioned toolstack-restart after the update could have helped me, but there was no info about that in the blog post warning ...

Here is the failed backup log:

    {
      "data": {
        "type": "VM",
        "id": "e93c337e-3532-c5fe-6442-25587d65c565"
      },
      "id": "1578874920072",
      "message": "Starting backup of Calypso (8341bb16-5e0f-42b8-ac81-a68ac532d42b)",
      "start": 1578874920072,
      "status": "failure",
      "tasks": [
        {
          "id": "1578874920072:0",
          "message": "snapshot",
          "start": 1578874920072,
          "status": "success",
          "end": 1578874931254,
          "result": "ab38fd4d-6d97-d630-f8d8-808b878a9c17"
        },
        {
          "id": "1578874931274",
          "message": "add metadata to snapshot",
          "start": 1578874931274,
          "status": "success",
          "end": 1578874931320
        },
        {
          "id": "1578874931449",
          "message": "waiting for uptodate snapshot record",
          "start": 1578874931449,
          "status": "success",
          "end": 1578874931676
        },
        {
          "id": "1578874932280",
          "message": "start snapshot export",
          "start": 1578874932280,
          "status": "success",
          "end": 1578874932280
        },
        {
          "data": {
            "id": "68c50187-ec00-45b8-9ada-fda127cf1d9c",
            "isFull": false,
            "type": "remote"
          },
          "id": "1578874932280:1",
          "message": "export",
          "start": 1578874932280,
          "status": "failure",
          "tasks": [
            {
              "id": "1578874932377",
              "message": "transfer",
              "start": 1578874932377,
              "status": "success",
              "end": 1578879743091,
              "result": {
                "size": 19443764736
              }
            },
            {
              "id": "1578879743101",
              "message": "merge",
              "start": 1578879743101,
              "status": "failure",
              "end": 1578882356886,
              "result": {
                "type": "TypeError",
                "message": "\"value\" argument is out of bounds",
                "name": "TypeError",
                "stack": "TypeError: \"value\" argument is out of bounds\n    at checkInt (buffer.js:1185:11)\n    at Buffer.writeUInt32BE (buffer.js:1278:5)\n    at Vhd._setBatEntry (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:236:16)\n    at Vhd._createBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:243:103)\n    at Vhd._writeEntireBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:265:30)\n    at Vhd.coalesceBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:319:20)\n    at <anonymous>"
              }
            }
          ],
          "end": 1578882356886,
          "result": {
            "type": "TypeError",
            "message": "\"value\" argument is out of bounds",
            "name": "TypeError",
            "stack": "TypeError: \"value\" argument is out of bounds\n    at checkInt (buffer.js:1185:11)\n    at Buffer.writeUInt32BE (buffer.js:1278:5)\n    at Vhd._setBatEntry (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:236:16)\n    at Vhd._createBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:243:103)\n    at Vhd._writeEntireBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:265:30)\n    at Vhd.coalesceBlock (/opt/xen-orchestra/packages/vhd-lib/dist/vhd.js:319:20)\n    at <anonymous>"
          }
        },
        {
          "id": "1578882356898",
          "message": "set snapshot.other_config[xo:backup:exported]",
          "start": 1578882356898,
          "status": "success",
          "end": 1578882356907
        }
      ],
      "end": 1578882361453
    },

Same problem here with current stable xo-server 5.53.0, xo-web 5.53.3 (build from source).
I also increased the virtual disk of the VM a week before.

@asai, @julien-f are ther any news regarding this issue?