So I used the TM backup from my old 2009 macbook to restore my 2010 macbook. It worked great and running sierra as my old machine was. But I have 22.63GB of purgeable data. What is this? I plugged in the time machine drive to make a new backup as going to install an SSD. Now sierra does not see the TM drive at all. now between recovering from the TM drive and moving across the data from the macbook pro I been using for work and plugging the TM drive back in.... it upgraded to 10.12.2 Has this update messed it up? even disk utility cannot see the drive now! it worked as i recovered from it. Plugged drive into my imac and it works. so looks like a sierra thing?