Q: Migration Assistant in Mavericks does not allow User account migration

When Migration assistant starts, it logs out of any users and unmounts all disk volumes.  You can SSH into the target machine, or the host machine if attached by a USB or similar and run the following commands to manually mount the disks:

sudo diskutil mountDisk /dev/disk1s1

sudo diskutil mountDisk /dev/disk1s2

you can check that these are now mounted with

sudo diskutil info /dev/disk1s1

sudo diskutil info /dev/disk1s2

Found the solution with more information here:

http://www.hardturm.ch/luz/2014/02/fixing-os-x-10-9-mavericks-migration-from-ext ernal-volume/

After a similar problem I found http://www.hardturm.ch/luz/2014/02/fixing-os-x-10-9-mavericks-migration-from-ext ernal-volume/ which explains that since Migration assistant logs you out, it also unmounts external disks. As AtlNCS Admin points out, they have a solution in using ssh and command line stuff to mount the needed disk remotely, but someone in the comments had a simpler solution: do not plug in the external firewire disk until after launchine Migration Assistant. So before running MA, eject the external disk that you want to migrate to the new machine (and unplug it) then start Migration Assistant and after selecting "migrate from an attached disk" THEN plug in the disk. It worked for me.