i currently have El Capitan on my MBA early 2015 with 8g ram and 250g memory. My TM is old HD with 500g storage. Everything works great and I have backups of my OSX and data on my TM. If I update to High Sierra I understand that my file system will be converted to APFS. I read that I do not need todo anything to my TM after I install High Sierra. However, my TM will have a different file system than High Sierra. My questions are 1. What happens after the High Sierra installation, when I do a TM backup of the High Sierra OSX and APLS data to the TM? I heard that it will be very time consuming because the TM will treat all the High Sierra data as new data, and I will probably run out of TM space. 2. What happens when I need to restore my High Sierra data TM backup? How does this work with High Sierra? 3. Assuming I will have enough space, should I keep my El Capitan TM backup? Thank you in advance for your help.