How to Fix Mac Startup Disk is Full

By Amanda | Posted to Home > Howto, on September 18th, 2021

Summary: This post tells you what to do when the Mac says "Your disk is almost full," including how to check storage, how to manage and clear storage. Apply these methods to get rid of the Mac startup disk full issue.

Mac startup disk is full

The Startup disk is the hard drive where the computer's operating system and applications are installed. For most Mac users, there is only one disk physically built in your Mac, so the unique disk is the startup disk. All your data are kept on it.

Over time, the stored files on your Mac's startup disk pile up, and the available storage space has become less and less. This post aims to help you clean up your Mac in multiple ways and reclaim more free space to use.

If you fail to update macOS or want a clean reinstallation, you can format Mac startup disk to get a brand new drive to use.

What does "Your disk is almost full" mean

This dread warning will appear on your Mac when the space of Mac's startup disk is going to be full. It is annoying. Worse, with a large amount of storage was occupied on the startup disk, Mac may fail to upgrade macOS, run slowly, or behave abnormally. Therefore, you need to take measures to avoid seeing this error again.

target disk mode on M1 Mac

How to check storage on Mac

If you want to know how much space has been used and how much space is available on the startup disk, you can check it within a few steps.

  • Click the Apple logo in the top-left corner of your screen.
  • Select About This Mac.
  • Click Storage and wait for the chart to load.

Under the name of your startup disk, it says how much space is available. And there is a bar divided into several blocks, representing different categories of files. You can hover your cursor over the chart to find out how much space each category is using.

check startup disk storage on Mac

How to manage storage on Mac

As you can see, there is a Manage button on the storage panel. Click the button, you will see a new window with recommendations on what you can do to optimize storage. Let's dive into it together.

Store in iCloud: You can choose to store all your files, photos, and messages in iCloud. With this feature enabled, the original of your files will upload to iCloud. All of them are available on all your devices with the same Apple ID. And only the recent files and optimized version of photos will be kept on your Mac when storage space is needed.

Optimize Storage: It will remove all the movies and shows you have already watched from your Mac. You can download those movies and shows again when you need them.

Empty Trash Automatically: When a deleted file lays down in the Trash for more than 30 days, it will be removed from the trash automatically.

Reduce Clutter: Click Review files, system will sort out your files by Large Files, Downloads, Unsupported Apps, Containers, Files Browser. Click each category and delete unnecessary files.

manage storage on Mac

How to free up space on Mac

In addition to Mac's recommendations, there are some other proven methods to free up space on Mac. Some files are easy to delete such as music, movies, videos, ect., while some are not.

The greyed column among the whole storage bar are files that macOS can't categorize to any known forms, called 'other storage.' Follow this guide on How to Delete 'Other' in Mac Storage to Free up Mac Space, you can dive under the hood of Mac, find out and delete junk files that waste space. The proven methods include:

  1. Clear temporary files
  2. Clear cache and log files
  3. Delete unwanted Downloads
  4. Remove outdated backup files
  5. Delete disk images and archives
  6. Clear unnecessary plugins and extensions
  7. Delete any unwanted files

FAQ

Why can't I find startup disk on my Mac?

Some Mac users encounter the internal hard drive not showing up on Mac issue at startup or after boot. You can try to use macOS recovery mode or First Aid in Disk Utility to handle it. In case the startup disk is corrupted, run iBoysoft Data Recovery for Mac to rescue lost files.

How do I wipe my Mac startup disk?

Step 1.Restart your Mac, and press Command + R, while it's restarting.

Step 2.Select Disk Utility from the macOS Utilities menu.

Step 3.In the sidebar, choose Macintosh HD.

Step 4.Click the “Erase” button, then select a file system format and enter a name for it.