Mac available disc space rapidly going down (MacBook Pro OS X El Capitan)

You should never run a mac with only some 2GB of free disk space.

Your sleepimage file alone would be 8GB.

It is usually recommended that each drive have at least 10% free space, more if it is the system drive.

Do you use video applications like iMovie or FCP X? Video files take a LOT of space.

An iMovie library or FCP X library can easily use several GB and would be classified as "other".

You can do a search in the Finder for files larger than a certain size.

It's probably Filevault—Apple's encryption system. Encrypting data on your computer uses additional storage, and it can go down rapidly in minutes, as you experienced. This is because each and every system file, cache, log, etc. is encrypted, essentially doubling the amount of used space.

On my MacBook Pro 2015, I had this enabled without my knowledge, and my storage was also rapidly decreasing. I didn't know what to do. I discovered the problem when I plugged in power, which is required for Filevault to encrypt data. I wanted to turn it off, but decryption was required—a process that takes hours to complete.

In the end, I reset my Mac to factory settings with a backup of my drive, meaning I could disable this in the setup next time. If this is the problem, try decrypting your drive, and hopefully, you will gain easy storage.

If you don't know how:

*Go to System Preferences

* Go to Security and Privacy

*Click on File Vault, press the lock at the bottom of the window to authenticate, then turn it off to begin encryption.

All Filevault does is encrypt the contents of your disk and make one administrator password required to access your files if unaccessible. So if your computer glitches and your password can't log you in, or you forget that password, you cannot access your files at all.

Alternatively, to protect my files, I back up to an external hard drive either manually or through Time Machine. It works great. Apple's Filevault doesn't suit me since I don't have a large hard drive (128 GB) and I am not in a business, so my files do not need to protected in this manner.

I will write a follow up to this if you have any questions. But this should help you. If Filevault isn't enabled, I advise you book an appointment at the Genius Bar to run their diagnostics, because this should not be happening!

For information about the Other category in the Storage display, please see this support article. If the display seems to be inaccurate, try rebuilding the Spotlight index.

Empty the Trash if you haven't already done so. If you use iPhoto, empty its internal Trash first:

iPhoto ▹ Empty Trash

In Photos:

File ▹ Show Recently Deleted ▹ Delete All

Do the same in other applications, such as Aperture, that have an internal Trash feature. Then restart the computer. That will temporarily free up some space.

According to Apple documentation, you need at least 9 GB of available space on the startup volume (as shown in the Finder Info window) for normal operation—not the mythical 10%, 15%, or any other percentage. You also need enough space left over to allow for growth of the data. There is little or no performance advantage to having more available space than the minimum Apple recommends. Available storage space that you'll never use is wasted space.

When Time Machine backs up a portable Mac, some of the free space will be used to make local snapshots, which are backup copies of recently deleted files. The space occupied by local snapshots is reported as available by the Finder, and should be considered as such. In the Storage display of System Information, local snapshots are shown as Backups. The snapshots are automatically deleted when they expire or when free space falls below a certain level. You ordinarily don't need to, and should not, delete local snapshots yourself. If you followed bad advice to disable local snapshots by running a shell command, you may have ended up with a lot of data in the Other category. Ask for instructions in that case.

See this support article for some simple ways to free up storage space. A common waste of space is old iTunes backups of mobile devices. As illustrated in this support article, select the Devices tab in the iTunes preferences window, select the backups you want to delete, and click Delete Backups. Keep at least one backup of each device that you still use.

You can more effectively use a tool such as OmniDiskSweeper (ODS) to explore the volume and find out what's taking up the space. You can also delete files with it, but don't do that unless you're sure that you know what you're deleting and that all data is safely backed up. That means you have multiple backups, not just one. Note that ODS only works with OS X 10.8 or later.

Deleting files inside a photo or iTunes library will corrupt the library. Changes to such a library must be made from within the application that created it. The same goes for Mail files.

Proceed further only if the problem isn't solved by the above steps.

ODS can't see the whole filesystem when you run it just by double-clicking; it only sees files that you have permission to read. To see everything, you have to run it as root.

Back up all data now.

Install the app in the Applications folder as usual. Quit it if it's running.

Triple-click anywhere in the line of text below on this page to select it, then copy the selected text to the Clipboard by pressing the key combination command-C.

security execute-with-privileges /A*/OmniDiskSweeper.app/*/M*/* 2>&-

Launch the built-in Terminal application in any one of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Paste into the Terminal window by pressing command-V. You'll be prompted for your login password.

The application window will open behind other open windows. When you scan a volume, the window will eventually show all files in all folders, sorted by size. It may take a few minutes for the app to finish scanning.

I don't recommend that you make a habit of doing this. Don't delete anything as root. If something needs to be deleted, make sure you know what it is and how it got there, and then delete it by other, safer, means. When in doubt, leave it alone or ask for guidance.

When you're done with the app, quit it and also quit Terminal.

Hello _Kat_M,

You need more free disk space. With a 256 GB SSD, I recommend no less than 50 GB free. Eventually that will start to get used up. Once you get down to 25 GB free, you will need to take action to free up disk space.

The problem is that if you actually do run out of disk space, it is very difficult to recover. You shouldn't wait until get the "startup disk is almost full" message. With 8 GB RAM and an SSD, you can fill up 8 GB of disk space instantly. You were just lucky this time. As you noticed, whether or not you have any apps running is irrelevant. In a modern version of OS X, you have literally hundreds of apps running in the background at all times. Many of these tasks are uploading and downloading files in the background. You could run out of space on your Mac and think you'll just use your iPad until you get a chance to clean it up. But using your iPad will create new files and upload them in the cloud. Your Mac will then download them and run out of disk space.