Managing locally a Time Machine backup

Time Machine can use a NAS server to save its backups. But then it can be very very slow.
When you need to save a large amount of information, it is better to connect the disk directly on the Mac, and open the xxx.sparsebundle image where is located the backups.

Stop saves in timemachine.

Then in terminal, do:
sudo tmutil setdestination
and drag from finder the disk that is shown. You will have something like:
sudo tmutil setdestination /Volumes/xxxxx

Then press enter, and in timemachine, said save now

When it will be done, connect again the disk to the NAS