The chia plotting process involves four phases of writing/reading to your drive through a temporary chia folder. Once all phases are completed then the temp file is renamed to a final .plot file and moved onto a slow drive for the farming process.
The first phase generates all of your proofs of space by creating seven tables of cryptographic hashes and saving them to your temporary directory. Phase 2 back-propagates through the hashes, phase 3 is a sort and algorithmic compression of these hashes in the temporary directory. Also, the final file is started and in the phase 4 completes the file and moves it into your final plot destination.
Generating the initial plot file is the most time consuming 6-12 hours depending on sustained write speed of the disk for your temporary directory. However, keep in mind that a total of almost 2TB will be written in the process of generating a plot file.
A final plot file will be about 101GB but require 239GB of total drive space.
Don’t use your OS boot drive as the temporary location to do read and writes as it will wear out the drive too quickly. Instead, get a second drive that you will consider will eventually expire within a few months and do not expect your drive manufacturer to honor your warranty if you use Chia with it.