Root is now nvme/ROOT/pve-1. The USB DOM keeps the ESP and /boot but is
out of the runtime I/O path, so a bus reset can no longer drop root from
under a running hypervisor. All five guests healthy, three pools ONLINE,
system running, ext4 pve-root intact and unmounted as the rollback with
its own kernel and initrd. zfs-import-cache is now the active import
path -- the all-three-pools cachefile fix doing its job.
The window cost an unplanned outage, and the cause was this repo's own
tooling rather than the migration.
The staging chroot ran `mount --rbind /dev` and /sys with no
--make-rslave. On systemd `/` has shared propagation, so the cutover's
`umount -R` propagated back into the live host and removed the real
/sys/fs/cgroup, /dev/pts and /dev/shm. With cgroup2 gone systemd-logind
could not create a session: ping fine, TCP fine, SSH authentication
succeeded, resident daemons kept serving -- and every new exec hung,
including /sbin/reboot, so the reboot never ran at all.
It impersonates failing root-disk I/O almost perfectly, and I called it
as the DOM dying. That was wrong. dmesg had the answer throughout: the
DOM attached cleanly with no errors, and the last log timestamp was
12114881s -- 140 days -- meaning this was still the original boot. A
down-detector had also never reported the host down, which I read as a
fast reboot rather than as no reboot.
Fixes and guards:
- --make-rslave after every rbind, plus a guard that refuses to proceed
while any chroot bind still reports shared propagation.
- Confirm a reboot by observing the host DOWN, not by watching for it to
come back. Those two states are indistinguishable otherwise.
- Blast radius now measured from the server: `ss` inside CT 103 found
five NFS clients, not the two documented. The new one that mattered is
esh-vm-db, hard-mounted and unreachable by ssh. Left mounted on
purpose and it came through read-write.
- grub-reboot's one-shot does NOT work here: grubenv sits on an LVM LV
which GRUB reads but cannot write, so next_entry survived the boot
that consumed it. Steady state is saved_entry=pve-zfs-root with no
next_entry. There is no auto-fallback on this host and no IPMI.
Recovery needed no console: an idempotent cgroup2/devpts/shm remount
landed in the brief windows where exec succeeded. No data was lost, and
neither the DOM nor any pool was ever at risk.
