I downloaded Sierra last night and have about 3.5 GB of available space left on my 2012 rMBP. When I attempt to install Sierra, it goes through a 2-minute "preparing to install" process, then launches into the update, whereupon the update halts and a message says Sierra can't be installed because there isn't enough space available. Does anyone know how much more space I need, beyond the 3.5 GB I have, in order to install Sierra? I'm planning to buy a new MBP soon with a bigger HD, which will solve the lack of space issue, but I'd like to get Sierra installed on my current machine. Thanks.