@TrapoSAMA You can build XO from sources and have full access to all. You may use my script if you like - https://github.com/acebmxer/install_xen_orchestra

@florent Running delta backup with CBT to S3. NBD connections=1 Yes, NBD. No VHD only. Yes, NBD is enabled and working on all pool hosts. Yes, XO can access the network used for NBD. No, a default backup network as not been assigned. No more logs from journalctl. My normal large nightly delta backup to S3 ran and did not produce any new errors. So far, just the one error once.

@acebmxer all good and thank you again for sharing your discovery on the forums

All hosts are restarted with 9.2.18 loaded now. Will see what happens next. [15:56 ovbh-pprod-xen05 ~]# drbdadm --version DRBDADM_BUILDTAG=GIT-hash:\ 71c8bcff6ea77a022b272a7eba649a774251bac4\ build\ by\ @buildsystem\,\ 2025-11-03\ 10:21:36 DRBDADM_API_VERSION=2 DRBD_KERNEL_VERSION_CODE=0x090212 DRBD_KERNEL_VERSION=9.2.18 DRBDADM_VERSION_CODE=0x092100 DRBDADM_VERSION=9.33.0

Hello @anthoineb, Thank you. I have attached the requested evidence as separate text files because the forum does not accept ZIP archives: two complete GDB/tap-ctl captures taken during the same incident, before reboot; the corresponding daemon.log excerpt from the hypervisor; the corresponding SMlog excerpt from the hypervisor; a README containing the timeline and identifiers; SHA-256 checksums. Both host-log excerpts cover 2026-07-25 04:35:00-05:10:00 MSK (UTC+03:00). The first GDB capture started at 04:45:44, the independent repeat capture started at 04:48:03, and the forced VM reboot was requested at 04:58:33. Both captures show the same state: the tapdisk main thread was in scheduler_wait_for_events(); n_reqs=32 and n_reqs_free=32; req_prod=req_cons=rsp_prod=rsp_prod_pvt=0; tap-ctl reported reqs_outstanding=0; the guest still reported 31 requests in flight and all 32 blkfront tags busy. The host logs contain no tapdisk error before the reboot. At 04:58:34-04:58:36 they show the expected sring disconnect, tapdisk close/detach and clean shutdown after the forced reboot request. The new QCOW2 tapdisk was opened at 04:59:57 and its sring connected at 05:00:27. Please let me know if you need another structure printed from GDB or a wider host-log interval. Our recovery controller can preserve the same pre-reboot diagnostic window during the next occurrence. SHA256SUMS.txt README.txt osott-193-SMlog-20260725-0435-0510.txt osott-193-daemon-20260725-0435-0510.txt 20260725-044732-gdb-172.30.52.193.txt 20260725-044544-gdb-172.30.52.193.txt