> you'll get IO errors, and then the IO errors will go away once the migration completes but your disk will be empty.
This seems extremely dangerous as nothing notifies the OS to unmount the filesystem and flush its caches, leading to trashing of the new disk as well. The only way to recover would be to manually unmount, drop all IO caches, then reformat and remount.
When standard filesystems like ext4 and xfs hit enough io errors,they unmount the filesystem. I find that this happens pretty reliably in AWS at least and I can't imagine the filesystem possibly continuing to do very much when 100% of the underlying data has disappeared.
That said, from further reading of the GCP docs, it does sound like if they detect a disk failure they will reboot the VM as part of the not-so-live migration.
This seems extremely dangerous as nothing notifies the OS to unmount the filesystem and flush its caches, leading to trashing of the new disk as well. The only way to recover would be to manually unmount, drop all IO caches, then reformat and remount.