Recommended MINIMUM free disk space on Mac booting and non-booting disks?

In the event you should ever become confused by some of the mythology that continues to be parroted on this site with disturbing regularity, I suggest you install macOS on a small (30 GB for example) partition, and see for yourself if the popular claims of 10%, 15%, or some equally arbitrary number of bytes is justified.

I did that and ran Mavericks for a solid week with less than a couple MB free space, sometimes half a MB, and on occasion with not a single solitary byte available. Not one.

What happened? Nothing. The Mac booted and ran just fine with no sluggishness whatsoever, without even the slightest perceptible performance degradation. It was a disappointingly boring test.

I don't have a screenshot, because there was no disk space available to save it.

So I took a photograph:

Oh just to keep things interesting Mavericks was running on a 30 GB iPod:

After a week of boredom the novelty wore off and I restored the iPod to its usual service.

Conclusion: As I wrote don't worry about it. If macOS needs more disk space for it to work, it will tell you.

Yes and watch out for background downloads.

Apple loves packing those into your workflow, with iTunes, iCloud, photos, music, videos, browsing, Podcasts, background downloads etc.

You can sometimes see that safe margin vanish overnight.

Peter

The rule of thumb I've heard is usually 15% free space. Of course this can vary depending on the size of the disk. (a 10TB disk will require a much smaller percentage) Also a disk with an OS on it needs more free space to operate efficiently than a storage disk. Generally, the more free space the better. I'd go with 100MB minimum in all cases to be safe.

I have read 10% free space on booting disks, but does is it also apply to large 10TB disks?

Of course not, for the reasons you expressed. Any percentage value is arbitrary and unjustifiable, regardless of the disk's capacity.

There is no specified minimum, unless you need to reinstall macOS, in which case it will need enough to do that, just as any Mac needs sufficient resources to do whatever your various programs require. Those amounts cannot be summarized in some arbitrary percentage.

macOS needs sufficient free space to do what it needs to do. A number of actions and dedicated processes are invoked when free space becomes insufficient. Those actions occur automatically and without any user intervention. If macOS needs additional help from you to accomplish that, it will tell you. If that should occur, the warnings it presents must not be ignored. If you were to ignore those increasingly strident warnings, you may find yourself with a Mac that won't boot.

10% is recommended but in practice I found 15% is better.

Haven't tried a 10Tb disk yet but would love to. 🙂

And I am unlikely to if that 10Tb disk is a Seagate. Won't touch them with a barge pole. Burnt too often.

Simple answer: If your Mac gets sluggish, back up whatever you can and free up some more space. It is only a problem if you get so full and your Mac so slow, that the Backup procedure takes forever.

Peter

Not mythology. Just experience. Lots of it.

I regularly run out of Hard Drive space on my Mac and it gets extremely unpleasant and you can waste the rest of the day fixing it. Better to not wander too close to the Black Hole. You may not know exactly what point that is because it all depends on what RAM hungry and Virtual Disk hungry App you may open to kick it off. Or simply open too many tabs in your browser combined with ll your other open Apps and your Mac's Activity.

It doesn't affect non-boot disks so much as your OS is not running off those, but if you have large files and fragmented small spaces left on a Volume, saving and opening will of course be affected.

Interesting that in my experience Windows 10 handles low volume storage much better. It is crap at other things but this is one thing I give it good marks for.

Peter

I will add my 2 cents re. empty drive space......... if you regularly edit/render videos or graphics using pro apps, then the recommendation is to have at least as much empty space as you have temp files in your project. This process is very processor intensive work and makes it easier if there is enough empty space available for the temporary placement of the files in the rendering process. I can easily amass 100 - 150 GB of temp files working on a one hour HD project, so I keep a larger amount of my hard drive available/empty. I usually either archive and/or dispose of those files when I am done with the project.

Important: Monitor Hard Disk Free Space | Larry Jordan

ApMaX wrote:

Thanks for the replies for Mac booting disk. But what about non-booting disks used just to store files? What would be the recommended MINIMUM free disk space for them?

The answer is similar – you need enough free space to store whatever you want to store, without the complications of also having a resident operating system sharing that volume for whatever it needs to store.

Nothing more than that is required:

Csound1 wrote:

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That is unless you are using an external disk as a scratch disk for such apps as Logic, Final Cut, etc. - or as the location for the iMovie, iTunes, Photos libraries where space needed would be ever changing.

Somewhere around 15GB is enough. 10% is ludicrous.

Ahh yes, I have every option in the App Store Pref Pane UNticked. No automatic downloads here. I check manually about once a week.

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