I wonder (after another failing live migration):
Which VM attributes (properties) are copied from source to destination when a live migration of a PVM is being performed?
In our case the libvirt framework is being used in a pacemaker cluster.
Specifically I'm wondering about:
- block-device assignments
- memory size
- number of vCPUs
- networks (veth)
- CPU model
A recent failure I saw was this:
The swap device of a VM was changed from LVM LV to separate disk, so the new disk had been added via block-attach while the obsolete LV was removed in the VM.
The VM configs that the pacemaker cluster uses were updates on each node (but libvirt seems to have its own copies in RAM).
The VM ran fine until it was live-migrated:
There were some error messages, but the VM continued for another 40 minutes until it stopped writing to systemd journal.
On the console I saw repeating messages like these:
[94124.120477] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 232s!
[94154.815980] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 263s!
[94185.599474] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 293s!
[94216.278977] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 324s!
[94247.062530] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 355s!
[94277.682031] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 386s!
[94308.401531] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 416s!
[94339.157047] BUG: workqueue lockup - pool cpus=0-1 flags=0x5 nice=0 stuck for 447s!
Actually the new VM lacked the separate swap disk.
But instead of panic-ing (and rebooting) the VM seemed to wait for something that would not happen.
After reboot I found these messages in jurnal:
Mar 23 20:02:19 v04 kernel: Freezing user space processes ... (elapsed 0.008 seconds) done.
Mar 23 20:02:19 v04 kernel: OOM killer disabled.
Mar 23 20:02:19 v04 kernel: Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
Mar 23 20:02:19 v04 kernel: PM: freeze of devices complete after 0.562 msecs
Mar 23 20:02:19 v04 kernel: suspending xenstore...
Mar 23 20:02:19 v04 kernel: PM: late freeze of devices complete after 0.104 msecs
Mar 23 20:02:19 v04 kernel: PM: noirq freeze of devices complete after 13.428 msecs
Mar 23 20:02:19 v04 kernel: xen:grant_table: Grant tables using version 1 layout
Mar 23 20:02:19 v04 kernel: Suspended for 1.170 seconds
Mar 23 20:02:19 v04 kernel: PM: noirq restore of devices complete after 0.166 msecs
Mar 23 20:02:19 v04 kernel: PM: early restore of devices complete after 0.085 msecs
Mar 23 20:02:19 v04 kernel: vbd vbd-51744: 2 reading other end details from device/vbd/51744
Mar 23 20:02:19 v04 kernel: xenbus: resume (talk_to_otherend) vbd-51744 failed: -2
Mar 23 20:02:19 v04 kernel: dpm_run_callback(): xenbus_dev_resume+0x0/0x130 returns -2
Mar 23 20:02:19 v04 kernel: PM: Device vbd-51744 failed to restore: error -2
Mar 23 20:02:19 v04 kernel: PM: restore of devices complete after 9.374 msecs
Mar 23 20:02:19 v04 kernel: OOM killer enabled.
Mar 23 20:02:19 v04 kernel: Restarting tasks ... done.
...
Mar 23 20:40:26 v04 systemd-logind[1034]: Failed to start session scope session-117.scope: Connection timed out
-- Reboot --
So likewise assume I've extended the VMs RAM while it was running.
Will the RAM vanish after being live-migrated, or will the RAM setting be "copied over"?
