A full startup disk is something that every Mac user will experience. This problem used to be known as “Startup disk full” notification. However, on newer macOS versions this message has been changed to “Your disk is almost full.”

• How To Free Up Disc Space On My Mac
• How Can I Get More Disk Space

Cleaner One Pro is your all-in-one disk cleaning manager. You can visualize, manage and free up your storage space in just a few clicks. Starting with a Smart Scan for your Mac, you can also take advantage of the Big Files detector, Duplicate Files and Similar Photos finder to delete all the useless junk files and free up more space. The Optimized Storage features of your Mac help you save storage space by storing your content in iCloud and making it available on demand: When storage space is needed, files, photos, movies, email attachments, and other files that you seldom use are stored in iCloud automatically. When there is too little free space on your hard drive, the computer’s work may slow down and show a poor performance. Thus, you should keep track of your Mac hard drive space usage and periodically clean it up. By knowing the disk usage information you can decide how much more space you need to speed up your Mac. Click About This Mac. It's the first option at the top of the drop-down menu. Click the Storage tab. It's the tab in the center next to the 'Displays' tab. Check the description under your hard drive. This will display how much free space is available on your hard drive in gigabytes (GB) under your hard drive's name (e.g '318.21 GB available of. How to free up space on a Mac? What is a “Mac Startup Disk”? Your Mac startup disk is a volume or a partition of a drive that contains a usable operating system. You can set your Mac to automatically use a specific startup volume, or you can temporarily override this choice at startup.

But luckily, it’s a problem that has many solutions. And in this article, we’ll go over:

• What is startup disk full?
• What's causing 'Your disk is almost full' alert?
• How to fix startup disk full?
• How to prevent 'Your disk is almost full' problem?

However, we also understand that some people are short on time and just want to fix startup disk full. So, if you’re not really interested in what it is and why it happens, just skip the next two sections and head to “How to Clean Your Startup Disk”.

Or, even better, if you’re looking how to clear space on Mac, we’d highly recommend a utility called CleanMyMac X. It'll help you clean up gigabytes of disk space in just minutes (you can download it here).

Note: if you’re running a newer version of macOS, it has a built-in option of Optimized Storage that is supposed to solve the problem of the full hard drive by moving files into the cloud.

By clicking 'Manage' you can open the menu and see what Optimized storage offers. However, it moves junk and useless files to the cloud together with your files, and eventually, you end up paying for iCloud storage to store junk. So we still recommend getting CleanMyMac and actually dealing with extra files rather than simply moving them.

Now, with all that said, let’s get into what exactly “Your disk is almost full” means.

Understanding What “Your Disk is Almost Full” Means

What is a startup disk?

A startup disk, as taken from Apple Support article, is a volume or partition of a drive that contains a usable operating system. Still confused? Let’s break it down for you.

Your Mac hard drive consists of disks (or partitions). Each disk (or partition) has your Mac data on it, which consists of your operating system, applications, etc. Most Mac users have just one disk but power users may have two or more.

Let’s look at an example of a Mac with only one hard disk:

• Your Mac's hard drive is 500GB.
• It has one 'disk' on it, so all 500GB of storage is on that disk.
• The disk has an operating system (macOS Big Sur), and user data (apps, etc).
• And since you only have one disk, this is your startup disk: all 500GB.

A Mac with two disks will have the storage divided between them. The Mac drive with the OS on it is the startup disk while the other drive is just used for storage of files. It’s possible to have multiple startup disks, but most Macs will only have one. And for proper disk cleanup on Mac, all drives are just as important.

Why your disk is almost full?

This is easy. It’s a lot like why is your fridge full? There is no more space! Your disk is almost full and this is very bad news for any drive. A hard disk should never get beyond 85% capacity (especially a startup disk) as you will experience slowness and errors the further you get above that mark.

If your startup disk is full and you get a message of warning from your Mac, this is a serious indication that you need to clear up storage immediately.

What to do when your disk is almost full?

So how do you fix your almost full startup disk? The same way you solve the problem of a packed fridge - you need to clear up storage, of course. To make more space on your startup disk you will need to:

1. Delete files from your Mac.
2. Move files to an external hard drive or cloud storage.
3. Or install a second internal hard drive on your Mac.

So, now that we know what a startup disk is, we need to talk about how to fix it. Let’s take a closer look at your disk space to see exactly what is causing your disk to be almost full.

What’s Causing 'Your Disk Is Almost Full' Alert?

Short version: Take a look under-the-hood of your Mac.

Before we can see what is taking up space on your startup disk, first we have to find it:

1. Hover on the Dock at the bottom of your screen and open Finder.
2. Click on “Finder” in the menu bar at the top of your screen.
3. Then select “Preferences…”
4. In the window that opens, checkmark the “Hard disks” checkbox.

After selecting this box, your desktop should now show the hard disks on your Mac, in the form of icon(s), like this:

These are disks on your Mac that you can “startup”, this is because they have operating systems on them. If there is more than one of these hard disk icons that show up on your desktop, it means you’ve got multiple hard disks on your Mac. If you only have one, skip the down to “What is taking up all of my startup disk space?” section.

If you have more than one, continue with the next step:

Click on the Apple icon at the top left of your screen System Preferences > Startup Disk.
Here, again, you’ll find your hard disk(s); they’re probably named something like MainSSD or MainHD. It will also display “OS” and the version number of that OS. If you have more than one OS drive, your startup disk should be the one with the latest version of macOS running on it, but we’re going to make sure of that in the next step.

I only have one and it looks like this:

To make 100% sure that you know what drive is your startup disk, follow these steps:

1. Click on the Apple Icon in the menu at the top-left of your screen.
2. Select “About This Mac.”
3. Under macOS, you’ll find a version number. Mine is 11.01.1, like so:

See how my version number in the “About This Mac” window matches the number in my Startup Disk section? Yep — That’s my startup disk. Found yours? Good.

What is taking up all of my startup disk space?

Now that we’ve identified our startup disk, let’s take a closer look at how to clear up space on Mac:

1. Click the Apple Icon in the menu at the top-left corner of your screen.
2. Choose “About This Mac.”
3. Click Storage.
   Note: If you are running an older version of OS X you may have to first click “More Info…” and then “Storage”.

Take a look at my hard drive disk:

I’ve got 500GB of storage, and about 275GB of it is free.

How To Free Up Disc Space On My Mac

So, how big is your hard disk? How much free space do you have (if any — *gulp*)? And what’s taking up the most space? It is important to consider drive capacity and data storage needs for future storage plans — we’re not just here to fix the problem, for now, we’re going to make sure you never have this problem in the future as well.

Now that we have the knowledge, it’s time to take action and fix your Mac’s “Startup Disk Full” problem.

Let’s go over 11 things you can do to help fix 'your disk is almost full.' These should also give you other ideas as to how else to fix it — You know your Mac better than we do!

1. Clear system storage on Mac

System storage cleanup sounds like a serious undertaking. But, technically, it boils down to just one thing: having the courage to scrap the old files.

1. Search for large ZIP/RAR archives in Downloads.
2. Open your Desktop (Command + F3) and delete screenshots.
3. In Applications, sort your apps by size. Delete the largest ones.
4. Restart your Mac to free up RAM.
5. Get rid of system junk files with a free version of CleanMyMac X.

This app gives you lots of possibilities to free up space, especially when it comes to system junk. CleanMyMac X has been notarized by Apple, which basically means it's safe to use. And if you got 5 minutes, try this tool as it shows you where exactly your junk hides.

2. Clean up cache files on your Mac

Cache files are files that help your Mac run programs a bit more smoothly. Think of them like blueprints for a house: your Mac has the blueprints for how a program is supposed to load/run/look, so it loads it faster; without them, it’d be like building it from scratch. However, over time, these caches can start to take up some serious space. Periodically, removing them can help clear storage. And don’t worry, your Mac will create fresh, new ones after you restart your Mac. To remove caches:

1. Open a Finder window and select Go in the menu bar.
2. Click on “Go to Folder…”
3. Type in ~/Library/Caches
   Delete the files/folders that are taking up the most space.
4. Now click on “Go to Folder…”
5. Type in /Library/Caches (simply lose the ~ symbol)
   And, again, delete the folders that take up the most space.

Deleting cache files is generally safe for your Mac. And once you delete them, the applications and processes you run on your Mac will generate fresh, new ones. But, when deleting, worry more about removing them based on size rather than just removing all of them.

Also, you can check the /System/Library/Caches folder as well, but it might be better not to touch this folder without knowing what the items are. A utility that correctly cleans up these files (and pretty much everything else on this list) is, you guessed it, CleanMyMac X. It cleans up even your system caches with just a few clicks.

Oh, and once you’re done with this list, restart your Mac so it can create these new cache files.

Read more: How to Clear Cache on a Mac?

3. Get rid of localization files

Localization files are also known as “language packs.” Lots of apps come with other languages that you probably don’t need. To clear up space on your Mac, delete the ones you don’t need:

1. Open a Finder window.
2. Go to Applications.
3. Ctrl+click on an application.
4. Select “Show Package Contents.”

From here, go to Contents > Resources and look for files ending in .lproj. These are the languages your app has just in case you want to use it in another language, like Spanish (es.lproj). Drag the ones you’ll never use to the Trash.

Again, a safer alternative to this would be to use CleanMyMac X. It gets rid of all of them with a click. No digging through application folders, just a cleaner Mac.

Read more: How to Delete Language Files from macOS?

4. Delete duplicate files

Even if you have the most organized Mac on a planet, duplicates happen one way or another. It can be a file you’ve mistakenly downloaded twice or a mail attachment you’ve opened several times. Regardless of how they appeared, those files sit on your Mac and gobble up storage.

But finding and deleting them is a time-consuming process if you do it one by one. So here’s what you can do for a simple Mac disk cleanup:

1. Open the Finder app on your Mac
2. Move cursor over File and click New Smart Folder
3. Click the “+” button in the upper right corner and choose the type of files you want to see
4. Now sort them by name to quickly spot duplicates.

Remember to pay attention to the date of creation to make sure you keep the true original, not the copy.

While this is the best way to remove duplicates manually, it takes lots of your time and dedication. It’d be much easier to leave this to Gemini 2: The Duplicate Finder.

This app quickly scans your Mac for duplicate and similar files and allows you to delete them within minutes. It keeps your originals safe and helps you easily retrieve files deleted by accident.

5. Remove old iOS backups

Backups can tend to take up a lot of space. You can find and remove them by:

1. Launching a Finder window.
2. Clicking “Go” in the menu bar.
3. Selecting “Go to Folder…”
4. Then, type in ~/Library/Application Support/MobileSync/Backup/

Get rid of all the old, outdated backups your Mac has been storing for a bit more extra space.

6. Remove large and old files

Keeping many large files on your Desktop and in Documents slows down the system. And if you delete only a couple of these enormously large files, you can get half of your storage back.

Let’s open the familiar About this Mac pane once again. If you click Manage, you’ll see this window for sorting files.

While this instrument is good for finding large files, it misses a lot of things. See that “Other” category that takes up 38.GB?

To deepen your search for massive files, use this tool from CleanMyMac X. It’s called Large & Old files finder.

It’s much more helpful as it shows you lots of other categories of files, like Archives. The app breaks your files by Size and Last Used.
To see this instrument in action, download the free edition of CleanMyMac X. And click the Large & Old files at the bottom of the sidebar.

7. Remove unnecessary applications

This isn’t often overlooked, but definitely under-appreciated. Removing old, unused applications is a great way to get some extra space on your startup disk. Go through your applications folder and get rid of all the apps you rarely use. But make sure you remove them correctly, don’t just drag them to the Trash. If you do, you’ll leave behind tons of leftover parts and pieces, and we’re trying to get back startup disk space — It’ll kinda defeat the purpose, no?

This is another place we’d suggest using CleanMyMac X. To completely remove any application, just launch CleanMyMac X, click Uninstaller, select your application, and then click Uninstall. You won’t have to search all over for development junk that’s left behind when Trash’ing an application. It’s incredibly easy and saves you tons of time.

8. Move your Photos and Docs to the cloud

When your local storage is full to the brim, your Mac will start uploading this data to iCloud. But only if you have this setting enabled. Is your Photos app synced with iCloud already? Let’s check.

• Open Applications and find the Photos icon.
• Launch Photos and click on Preferences in the top menu.

Ticking the box iCloud Photos will connect your Photos library to iCloud. And what’s more important, if you select Optimise Storage, some part of your Photo library will be moved to iCloud. This way you macOS saves precious space. The free iCloud plan allows you to free up at least 5 GB worth of storage.

The similar logic applies to your Documents and other files. To set up the cloud backup with iCloud drive, go to System Preferences > Apple ID > iCloud.

9. Clean up your Downloads, Movies, and Music folders

Have a closer look at these three folders. You’d be surprised at how many downloads can accumulate when you aren’t paying attention. Clean out anything you don’t need (or don’t know) and organize the rest. It’ll take a load off your mind to know that there’s nothing excess there.

The Movies folder can be a pain, not because you’re searching through tons of files, but it can be difficult to choose what to delete. Personally, I never want to get rid of Top Gun. It’s amazing. I watched it 3 times in a row last weekend. But alas, sometimes you need to make sacrifices for the health of your Mac. Though, what you can do with movies you want to keep is to archive them. So, archive what you wish to keep and remove the rest.

How to archive/compress a file

Archiving a file doesn’t mean to store deeper into the abyss of your Mac — but to turn the file into something smaller, into a compressed file (like .zip or .tar). By archiving a file, you shave off some memory. Archiving is essential for things you want to keep on your Mac, but don’t often use, and helps you clear up some space. And that’s what this is all about right? We’re essentially doing the hokey-pokey on your Mac. To archive a file, just:

1. Ctrl+click the file you want to compress (recommended for movie files).
2. Select, “Compress .”

The last place to sweep through is the Music folder. Find and remove duplicate music files first, and then clean up all the songs you downloaded on a weird Sunday afternoon cleaning the house.

10. Clean your Desktop

“Clean my desktop… but why?” Because some people’s desktops are hard to look at, that’s why. Organize your desktop and get rid of the stuff you just don’t need on there. It looks better and helps your Mac act a bit faster (I don’t know the rocket science behind this one, but it feels too good to be false). Your Mac doesn’t waste time loading all those icons and junk, just… Just clean it, please.

11. Empty out the Trash (No, we’re not joking…)

Seriously: It may sound incredibly basic, but it could clear a surprising amount of storage. I forget to do it all the time. The thing is, that when you delete something, your Mac doesn’t remove it — it just moves it to the Trash. Plus, you’ve probably deleted way more than you realize, and all that could be sitting in the Trash, wasting space. So get rid of all that junk by emptying the Trash:

1. Ctrl+click your Trash in the Dock.
2. Select “Empty Trash.”
3. And click “Empty Trash.”

And, the easiest step is done.

A few more tips to clear storage on Mac

1. Manage your Optimized Storage

This option comes with your operating system starting macOS Sierra. Go to the Apple menu > About this Mac > Storage

Now, click on Manage to reveal the space-saving options:

2. Erase your Junk Mail

Open your Mail app, and click Mailbox in the upper menu. Here you can erase spam and already deleted items.

Full Startup Disk Prevention

We’ve cleaned up a few things on your Mac, and hopefully, it’s given you more ideas as to what else you can clean. But, let’s take a look at how much space you saved from cleaning the list above. Remember how we checked your Mac’s free space? Open that window again and see how much space you’ve cleared up:

1. Click the Apple Icon in the menu at the top-left corner of your screen.
2. Choose “About This Mac.”
3. Click Storage.
   Note - If you are running an older version of macOS you may have to first click “More Info…” and then “Storage”.

You’ve probably got a bit more space, and you’ll want to keep it that way. The only way to prevent a “your disk is almost full” is by keeping your Mac clean. We’d recommend a complete cleaning every 2–3 weeks.

Say goodbye to the 'Your startup disk is almost full” message.

We've told you how to delete storage on Mac in multiple ways. Hopefully, this has helped you fix that full startup disk problem. Your startup disk should now be quite a bit lighter (we hope). Oh, and if you liked this article, get social with it to help others in need. And if you really liked this article, subscribe to our email list — we’ve got more guides on the way. And we’ve also got a utility that’ll help you out a ton in the long run: CleanMyMac X. It helps you clean your entire Mac with just the click of a button. It’s incredibly easy to use and works like a charm.

Summary :

From this MiniTool article, you can know what the startup disk on your Mac is, what is taking up space on the Mac startup disk, the influence of startup disk full, and how to clear the startup disk space when the startup disk is full or your disk is almost full on your Mac.

What Is Startup Disk on Mac?

Like a Windows startup disk, the startup disk on your Mac is the disk that saved the operating system on your Mac. It is an important disk on your computer. If the operating system on the disk is corrupted or even the startup disk is damaged, your Mac computer will not boot normally.

What Is Taking Up Space on Your Mac Startup Disk?

As you know, a Mac computer’s disk is usually not as large as a Windows computer’s disk. As of 2020, Apple has improved the disk capacity and the maximum disk size can reach up to 8TB. But they are the Pro series, which are not widely used.

Most of the time, you should not worry about the disk space issue because macOS always do work online. This will not take up much disk space. However, what’s going on if you see a pop-up alert saying Your startup disk is almost full?

At this time, you should know what is taking up space on the startup disk of your Mac and then take some measures to clear the startup disk.

How Can I Get More Disk Space

The hidden website cache takes much space on the startup disk. For example, statistics show that Google Chrome can create numerous cache folders after you visit some web sites. The size of the cache for one site can even reach up to 9 GB. This is quite surprising, but it is true.

As time goes on, the free space on the startup disk becomes less and less. One day, you may receive the startup disk full alert.

Besides, when a warning of Your disk is almost full pops up, it also means that there is not enough space on your Mac. It is equal to startup disk full. Likewise, you need to remove some files to free up disk space on your Mac computer.

What Does It Mean When Your Startup Disk Is Full?

When does it mean when you receive your startup disk is almost full alert?

It has two main influences:

1. You will soon run out of space on the startup disk.

Your startup disk is almost full is an early warning for you. It reminds you of cleaning up the startup disk. However, if you continue to use your Mac without cleaning up disk space, more and more data will be saved to the startup disk. One day, your Mac will run out of space and you will not use the machine as normal.

2. Your Mac computer will run slowly.

Some of you may think that your Mac computer will not be affected when there is space in the startup disk no matter it is much or less. It is wrong.

A Mac computer can convert the available free space on the startup disk into virtual memory that you use for day-to-day operations. In theory, there should be at least 10% of free disk space for your Mac to operate. If not, your Mac computer will run slowly and even face big trouble like Mac frozen.

When the machine detects that the available space on the startup disk is insufficient, it will give you a warning. This aims to remind you it’s time to clear the startup disk on your Mac.

What should you do when your startup disk is full on your Mac? In the following part, we will show you some solutions.

How to Clear the startup Disk?

If you want to clear your Mac startup disk, you need to delete the unnecessary files on it. Before doing this, you can check the storage space on your Mac.

How to Check the Storage Space on Your Mac?

1. Click the Apple menu from the top-left corner of the screen.
2. Click About This Mac from the drop-down list.
3. Switch to the Storage section.

After these three steps, you can see the storage information of your Mac disk, including the files’ types, the free space on the drive, and more.

If your Mac Startup disk is full, you can do these things to free up disk space:

How to Clean the Startup Disk on Your Mac?

1. Remove the App Cache from your Mac.
2. Empty Trash.
3. Delete the unnecessary Time Machine backup snapshots.
4. Delete browser cache.
5. Remove language packs.
6. Use Startup Disk Full Fixer.

Tip 1: Remove the App Cache from Your Mac

The app cache files are necessary when you want to speed up processes. Once you complete the process, the cache files become useless. But these cache files will stay on the startup disk for a long time unless you manually delete them. When they are useless, they are junk files. To clean up your Mac startup disk, you need to remove them from the machine.

1. Go to Finder > Go > Go to Folder.
2. Type ~/Library/Caches.
3. Go into each folder and then delete the files in it. You can also choose to only delete the files that take up the most space.
4. You can repeat the above three steps for /Library/Caches to remove the App cache.

Tip 2: Empty Trash

When you delete files from your Mac, they will be moved to Trash. The files on Trash also occupy space on your Mac startup disk. As long as you are sure that you don’t need to use these files anymore, you can empty Trash to free up disk space.

To do this job, you just need to open Trash and then click the Empty button on the top-right side to remove files from your Mac. Since then, there will be more available disk space on your Mac.

Tip 3: Delete the Unnecessary Time Machine Backup Snapshots

Most people would like to use Time Machine to back up their Mac files to an external hard drive. You may think that the backup files are save to the external hard drive. But that’s not all. During the Mac data process, the local snapshots also automatically start once every 24 hours. That’s right. The snapshots are saved to your Mac, taking up disk space.

You can delete the unnecessary Time Machine backup snapshots to release space on the startup disk.

1. Open Finder.
2. Go to Go > Utilities.
3. Double-click Terminal to open it.
4. Type sudo tmutil disablelocal into Terminal, and press Enter.

Do you know how to delete Time Machine backups on your Mac computer? In this post, we will show you different cases and different methods.

Tip 4: Delete Browser Cache

Every time you visit a new web site using your web browser, some cache files will be created and saved to your Mac disk. This can help you to quickly a previous page again. But these files can also use up your disk space. So, you can delete these browser cache files to release more space on your Mac:

1. Open your web browser.
2. Click the History tab and then select Clear browsing data.
3. Select the cache files you want to delete like Cookies, site data, Cached images and files.
4. Choose how far back you want to delete
5. Click the Clear browsing data button to delete the selected cache files.

Tip 5: Remove Language Packs

Most apps contain language packs (which are also known as localization files). These packs allow you to switch between languages when using the app. They are useful, but you need to admit that you only need one or two languages. The rest language packs just waste your disk space. You can choose to delete them:

1. Open Applications.
2. Right-click an app and then select Show Package Contents.
3. Click Contents.
4. Click Resources.
5. Delete the language packs you don’t need to use. The pack files are ending in .Iproj.
6. Repeat these steps for all other apps on your Mac.

Tip 6: Use Startup Disk Full Fixer

Startup Disk Full Fixer is the best free app for you to perform a quick Mac disk cleanup. It can help you to get more free storage space in less than a minute. You can go to the Mac App Store to free download this application. Then, you can open it and use it to clean up your startup disk to get rid of the low disk space warning. It is a safe program. You can feel free to use it.

How to Free up Disk Space on Your Mac?

Your disk is almost full is another alert that prompts you to clear disk space on your Mac computer. We have published a related article to free up disk space on Mac: How to Clear Disk Space on Mac and Recover Mac Data?

If you have some other good ideas to release disk space on Mac, you can share them with us in the comment. We will appreciate that.

If You Delete Some Important Files on Your Mac by Mistake

As you can see, it is a file deletion process when you clear the startup disk on your Mac. During the process, you may delete some of your important files by mistake. Once these files are permanently deleted from your Mac computer, you will be unable to restore them from Trash. If you want to retrieve them, you can try the free Mac data recovery software: Stellar Data Recovery for Mac.

This software has a trial edition. You can use it to scan the Mac disk you want to recover data from and then check whether it can find the files you want to rescue. If yes, you can upgrade it to a full edition and then use it to recover all your needed files to a suitable location. You can go to the MiniTool download center to get this trial edition.

1. Open this software.

2. Select the data types you want to restore. If you want to recover all, you can turn on the button for Recover Everything.

3. Click the Next button to continue.

4. This software will list all the drives it can detect. Then, you need to select the drive you want to recover from. If you want to perform a deep scan, you need to switch the button for Deep Scan to ON.

5. Click the Scan button to start the scanning process.

6. When the scanning process ends, you can see the scan results. By default, these files are list by Classic List. There are two other lists including File List and Deleted List. If you only need to recover the deleted files, you can switch to Deleted List and then find your needed items.

7. This software allows you to preview files. You can just double-click on one file to preview it and confirm whether it is your needed file.

8. If you are sure this software finds your needed files, you can go to MiniTool official site to get a license of an advanced edition to upgrade this software. After that, you can select files and then save them to a suitable folder. Here, you need to know that the destination folder should not be the original one. Otherwise, the deleted files could be overwritten and become unrecoverable.

Bottom Line

When your startup disk is full or you see the alert of your disk is almost full on your Mac, you can just try the methods mentioned in this article to free up disk space and remove the warning. If you mistakenly delete important files, you can use Stellar Data Recovery for Mac to get them back.

Should you have any related issues, you can let us know in the comment. You can also contact us via [email protected].

Startup Disk Full FAQ