VM live migration fails with error "Disk of instance is too large"

Problem

• VM live migration fails with below error:

Bash

2023-07-05 08:49:27.243 ERROR oslo_messaging.rpc.server [req-3469f20e-b1ef-43d5-85a9-1976bace495c [e-mail] c435] Exception during message handling: nova.exception.MigrationPreCheckError: Migration pre-check error: Unable to migrate 3a8cc10a-e5a2-4507-952b-feff6ccd8262: Disk of instance is too large(available on destination host:-939524096000 < need:128849676288)
2023-07-05 08:49:27.243 TRACE oslo_messaging.rpc.server nova.exception.MigrationPreCheckError: Migration pre-check error: Unable to migrate 3a8cc10a-e5a2-4507-952b-feff6ccd8262: Disk of instance is too large(available on destination host:-939524096000 < need:128849676288)

Environment

• Platform9 Managed OpenStack - v5.4.0 and Higher

Cause

• The host has disk capacity over-allocated because of which migration throws this error even when the disk has sufficient space available.

Resolution

• Below command can be used to live migrate the VM:

Bash

# openstack --os-compute-api-version 2.25 server migrate --block-migration --live <HOST_ID> --disk-overcommit <VM_ID>