@skematicaDon't even think about defragging. This extract from http://www.macworld.co.uk/how-to/mac/how-defrag-speed-up-mac-os-x-2016-3600241/ explains why.
DO NOT defrag a Mac's SSD.
If you're using a newer Mac that comes with an SSD (Solid State Drive), there's no point in wasting your time defragging as they already have a built in maintenance process called TRIM. In fact, it's actually dangerous to attempt to defrag a SSD, which can reduce its lifespan.
In any case, SSDs operate in a different way to a traditional HDD, allowing quicker access with fewer issues making them the preferred option for modern systems.