Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
How To Defrag a Mac
Once you’ve made the change from a PC to a mac you might be blown away by the faster speeds you will get, but this will change over time. No matter how often you use a computer or how good you are at backing things up and keeping a clean computer disc fragmentation still occurs. This is a fact of computing life, and this is how all computers no matter if they are a PC or a mac saves and deletes files. Once you have deleted a file it doesn’t actually disappear from the computer, it is changed from a no-go zone to a place that can be overwritten. In this instance, a file that is deleted is just waiting for something to write over it. This is how you can restore deleted files, and this is also how fragmentation occurs.
Over time your mac will need to look in multiple places to find your files. If you have used your mac for many years or even just for a lot of different work in short amount of time your disk may be so fragmented that it starts to run very slowly. If this happens, you will need to defrag your mac.
There are two ways to defrag a mac, although some people say that the first way isn’t true defragmentation. The first way involves simply taking everything off of your mac and reinstalling the hard drives and the operating system. This isn’t the true process of defragging because you haven’t gone through and changed where everything is, but it will have the same end result- everything will be saved in the correct spot and your computer won’t have to look around as much when it opens a file.
If you want to truly run a disc defragmentation on your mac then you will need to buy a third party app. At the time of writing, Apple doesn’t have its own app that will defrag your mac. This is because they believe their OS is so well optimized that you shouldn’t need to defrag. However, Apple isn’t against you running your own defragmentation and there are many apps that will do this.
Before you defrag your mac you should backup your computer. Use Time Machine and Time Capsule to make sure that everything is safe and secure before you defrag the disc. The next thing to do is to make sure you feel comfortable with the defragging app you have. There are many free apps around but some work better than others. Talk to someone at the genius bar at the Apple store and get their opinion on the matter. Note that it will only be an opinion and likely they will be hesitant to say anything in case something goes wrong and you blame them.
The defragging process will take some time no matter how streamlined the process may appear. It’s best to do this at a point when you won’t need the computer for a while. Set it up on your home computer before you leave for work or let it run over night.
The end result should be a faster and sleeker mac.