" can't compute delta" & "can't connect through NBD, fall back to stream export" after 2026-07-28

probain

Since updating to XO from source on 2026-07-28 my backups have started showing issues:
Issue still persists on 2026-07-29 on latest commit (26c36) after the latest XCP-ng updates as well.

 can't compute delta OpaqueRef:4f676f19-a405-9bf7-ebb8-508240593020 from OpaqueRef:044a8fe1-7547-175f-612a-82e8df28524a, fall back to a full
 can't connect through NBD, fall back to stream export
 Backup fell back to a full

This happens to almost all of my VMs. But not on my Windows Server 2025 VM. Unsure if that is relevant though.

2026-07-27 didn't have any such notices.

Andrew

@florent @olivierlambert I also have the same issue. I see there have been a lot of XO updates to the backups. Maybe this is fixing a hidden problem?

CR works, but normal delta backups to S3 have the issue on some of the VMs (on a test run). All the VMs on this backup are Linux.

A second run of the same delta backups all worked. I'll have to see what happens for the normal nightly backup with a lot more VMs...

(edit fix logs):

 2026-07-28T23:17:34.544Z xo:xapi:vdi WARN invalid HTTP header in response body {
   body: 'HTTP/1.1 500 Internal Error\r\n' +
     'content-length: 318\r\n' +
     'content-type: text/html\r\n' +
     'connection: close\r\n' +
     'cache-control: no-cache, no-store\r\n' +
     '\r\n' +
     '<html><body><h1>HTTP 500 internal server error</h1>An unexpected error occurred; please wait a while and try again. If the problem persists, please contact your support representative.<h1> Additional information </h1>VDI_INCOMPATIBLE_TYPE: [ OpaqueRef:4a172cde-c772-2b6c-100d-f63ea5e4d842; CBT metadata ]</body></html>'
 }
 2026-07-28T23:17:34.552Z xo:xapi:xapi-disks WARN can't compute delta OpaqueRef:6ec8ab35-d377-cd33-ce94-72a7a4e9e3b0 from OpaqueRef:4a172cde-c772-2b6c-100d-f63ea5e4d842, fall back to a full {
   error: Error: invalid HTTP header in response body
       at checkVdiExport (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/vdi.mjs:39:19)
       at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
       at async Xapi.exportContent (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/vdi.mjs:263:5)
       at async #getExportStream (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/disks/XapiVhdStreamSource.mjs:123:20)
       at async XapiVhdStreamSource.init (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/disks/XapiVhdStreamSource.mjs:135:23)
       at async #openExportStream (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/disks/Xapi.mjs:186:7)
       at async #openNbdStream (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/disks/Xapi.mjs:97:22)
       at async XapiDiskSource.openSource (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/xapi/disks/Xapi.mjs:268:18)
       at async XapiDiskSource.init (file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/disk-transform/dist/DiskPassthrough.mjs:28:41)
       at async file:///opt/xo/xo-builds/xen-orchestra-202607281243/@xen-orchestra/backups/_incrementalVm.mjs:104:5
 }
 2026-07-28T23:17:34.553Z xo:xapi:xapi-disks INFO export through vhd

acebmxer

I deployed a new XO last night - for just because. No issues with backups for me as of now.