Is your Mac coming up with a message advising the startup disk is almost full, but you can’t figure out why? In this article we’ll examine how to find the space hogs on a Mac so you can clear the disk space needed.
Step 1: Find out which data types are taking up the space on your Mac
Go to the Apple Menu > About This Mac > Storage and see what category is consuming most space. If it’s Applications, Documents, Movies Music or Photos, proceed to Step 2. If it’s the System or Backups (such as in the screenshot below) proceed to Step 3.
Step 2: Use the storage management tools in macOS to locate and remove large media files you don't need
Click the Manage button in the window above and you’ll be able to browse the files on your mac by type (Applications, Documents, Photos etc). The largest files will be at the top so it’s easy to see if they’re large media files which might not be needed anymore.
These can be moved to external storage thereby clearing disk space on your Mac, or alternatively compressed by right-clicking the file in Finder and selecting Compress. This creates an archived copy as per the screenshot below.
Step 3: Download DaisyDisk or another third party application to find other data using lots of disk space
System and backup files aren’t visible via the macOS storage management tools. So if these categories are consuming lots of disk space then third party tools will be required.
DaisyDisk is a useful and well polished application suited to this task. Although not free, there’s a free trial available from the developer’s website which will likely be enough to help narrow down the storage issues you’re having. There are completely free applications designed for this too, such as Disk Inventory X, however they were built for older versions of macOS so outcomes may vary depending on macOS version.
Once DaisyDisk’s scan runs you’ll be presented with a visualisation of where the Mac’s disk space is being used up:
You might find that a big Google Chrome cache or Outlook data files are responsible for the disk space issues, in which case they can be cleared as required.
What if /volumes/Data/ is using heaps of space? This would most likely be caused by Time Machine backups. These large directories under /volumes/Data/ can be safely deleted (after showing hidden files in macOS) if you don’t care about your local Time Machine backups. Any remote Time Machine backups on a Time Capsule or external drive will remain even if the local ones are deleted.
If Hidden Space accounts for a big portion (100GB+) as it does in the screenshot above, this could merely be lots of cached system files stored on your Mac (as explained in this article). In itself this isn’t necessarily a problem as macOS should automatically purge these caches if the disk becomes completely full. So if theres’ a decent amount of free disk space left on your Mac (10-20GB or more) it’d be best to leave things be. If you really want to confirm this is the issue, simply copy some random big files onto the Mac and see if Hidden Space reduces.
However if your Mac’s storage is completely filled up (as in, no more files can be copied to it because of low disk space) and lots of it’s still being hogged by Hidden Space, go to Step 4.
If none of these are using much space, skip to Step 6.
Step 4: Repair your Mac's disk volume
Your Mac may be miscalculating disk space or holding onto cached files even when the space is needed for something else. In the case there’s lots of Hidden Space showing in DaisyDisk and your Mac won’t let you copy any more files to it, running Disk First Aid via the built in Disk Utility may rectify the issue:
If this doesn’t work go to Step 5.
Step 5: Manually clear System Caches
System caches are important to improve the performance of your Mac, however if they’re taking up an unusually large amount of space and won’t clear automatically when disk space is low, they can be cleared manually using a free third party application called OnyX.
If your Mac is still filled with system files after this, the only proper fix would be to reinstall macOS. Read this article on Apple’s website for specific instructions, and make sure to backup important files first. Try reinstalling macOS without erasing the disk, as it will keep your existing files thereby saving time. However if the issue remains afterwards you will have to erase the disk before installing macOS. If you need just a little extra disk space in the meantime check out some of the other methods in this article.
Step 6: Remove PowerPC architectures and unneeded language files
A few more GB of space can be cleared from your Mac by downloading a free application called Monolingual, which can remove PowerPC architectures and unneeded language files. Monolingual can be downloaded from Github.
So what are PowerPC architectures? These are architectures used before Macs switched to Intel processors, around 2006. Therefore unless you’re using some very obscure and old software there is no need to have them. Be sure to keep all of the Intel architectures though:
As for language files, simply remove any languages which you’ll never need to use on the Mac. By default some commonly used language files such as English, French and Japanese are left in. However if you’re unsure whether a particular language will be needed or not it’s best to keep it, as once removed reinstalling macOS is the only way to get them back. Fortunately most of the languages are just slight variations on the main ones, so these can be removed without any worry.
Hopefully this article has helped you clear some disk space on your Mac! If there’s any other methods that have worked for you please share them in the comments section below to help others out. Any questions about the methods discussed in the article, leave a comment too.