Settings > Migrate was a horizontal form of six switches without
explanations. The owner chose this layout from three rendered options:
the route on top as "From" (the source host) and "To" (the
destination select) side by side, a "Storage" card with
where each disk goes, a "Transfer settings" card with the switches in
two columns, each with a line saying what it does, and a footer.
Codex reviewed migration end to end; these are fixed:
- No Offline switch: the mode follows the VM's state, and one line says
which. A shut-off VM moved offline whether the switch was on or off.
- Live migration shows for a running or paused VM; Auto converge,
Compressed and Unsafe only for a running VM, the only state the
migration applies them to. Unsafe was offered for a paused or shut-off
VM and ignored.
- Unsafe says it skips libvirt's safety checks; Delete source files
says it deletes only the files of copied disks.
- A VM that cannot migrate anywhere (no other host, a state that does
not migrate, snapshots, host devices) gets the reason and a disabled
button instead of the disk plan and the switches; it learned that
after submitting.
- Migrate stays disabled while the destination did not answer or a disk
cannot go there; it was enabled after any plan.
A migration needed every disk on storage both hosts share: it was refused
when the destination lacked a disk file, and a file of the same name
there was taken for the VM's own disk.
The Migrate tab now lists the VM's disk files for the chosen destination.
For each disk it offers the destination's pools that keep disk files
(directory, filesystem and NFS pools). A disk on storage both hosts share
can also stay where it is.
A directory counts as shared when both hosts have it as a storage pool
and a marker file created on the source exists on the destination. A
directory the probe cannot tell is never taken as shared.
libvirt copies the chosen disks during the migration: migrate3 with
NON_SHARED_DISK for those targets, and destination and persistent
definitions naming the new paths, where libvirt creates the files.
- A shut-off VM is started paused for the copy and shut off on the
destination; its CPUs never run. Its UEFI variables are copied first,
as the destination would start from the firmware's template. If the
migration fails, the VM is shut off on the source again.
- Refused before anything changes, each disk with its reason:
- a disk neither shared nor given a pool, also one only the next
start's definition has;
- CD-ROM images, read-only or encrypted disks, formats other than raw
and qcow2, and disks with a backing file;
- a pool that is not of disk files, or that has a file of that name,
which libvirt would reuse and overwrite;
- two disks copied to one file.
- The job claims each copy's name in its pool, and the source volume.
- A failed or cancelled migration deletes the copies libvirt made, and
the UEFI variables copy, unless a VM on the destination has them.
- The source files stay and are named in the log. With "Delete the
source files of copied disks" they go, except one another VM or volume
uses; a failed delete is logged and the migration stands.
The NVRAM sharing check uses the same probe: a shut-off move stops when
it cannot be told, and the source file stays.
The API's migrate call takes disk_pools ({target: pool}) and
delete_source.
