Having problems figuring out how much free space is available on your Mac? You’re not the only one. With the arrival of macOS Sierra, Apple changed how the OS calculates free space on a Mac. The change has more than a few folks scratching their heads, wondering what’s going on, and why they don’t seem to have as much free space on their drives as their Macs are telling them they have.
Is It Free Space or Purgeable Space?
One of the easiest, and certainly the most colorful, ways to see the amount of space taken up by purgeable files is to launch About This Mac from the Apple file menu, and then select the Storage tab. You may need to wait a short time while your Mac performs a few calculations, but eventually you’ll see a colorful bar graph depicting how the space on your various drives is being used.
The bar graph displays the space used by files, divided into categories. With macOS, new categories have been added, including iTunes, GarageBand, and System, in addition to the existing Apps, Photos, and Other. But it’s the last two categories at the far right side of the bar graph that interest us: Purgeable and Free space.
Free space is what it’s always been; storage space on your drive that isn’t currently marked as in use, and is available to your Mac’s file system to use as it pleases.
Free space is what used to show up in a Finder window’s status bar as Available. You can see this for yourself by opening a Finder window and selecting any folder, Desktop, or item. In the status bar (if needed, use the Finder’s View menu to select Show Status Bar), you’ll see the number of items in the current window, followed by the amount of free space available.
With macOS, the amount of available space shown in a Finder window is no longer just the free space, but is instead free space + purgeable space, though the Finder still just refers to it as Available.
You can get a more detailed look at what Available really means by right-clicking the startup drive icon and selecting Get Info from the pop-up menu. Under the General category in the Get Info window, you’ll see an entry for Available that includes the purgeable space. As an example:
Available: 717.08 GB (15.72 GB purgeable)
Another place to see this with a bit more detail is in Disk Utility. Launch Disk Utility and select your startup drive from the sidebar. In the Disk Utility window, you’ll see a bar chart with Purgeable and Free space called out. Near the bottom of the window is a table that includes a cell with the text:
Available (Purgeable + Free): 717.09 GB
What Is Purgeable Space?
Purgeable space is files residing on your Mac that the system considers disposable without any warning to you. Some of the files in the purgeable category are items the system manages, such as the various caches. But others are files you have had a hand in creating, such as files you downloaded from the Internet and are residing in your Downloads folder. Other files that can be purgeable include any files stored in your iCloud drive, iTunes movies, videos, podcasts, iTunes U courses, GarageBand sound libraries, foreign language dictionaries, and some fonts.
You may also find that local Time Machine snapshots are always marked as purgeable. You can find out more about Time Machine local snapshots at Apple’s support site.
Can I Delete Purgeable Files Myself?
Not easily. The first problem is that there’s no user interface available for seeing which files are marked as purgeable and which ones are not. If there was, then you could easily delete them yourself.
Can I Prevent a File From Being Marked Purgeable?
Not directly. Files you’ve used recently aren’t marked as purgeable, so that’s one way to ensure a file is never deleted by the system. But there’s not a “Do Not Purge” switch you can set.
How Do I Get a Purgeable File Back?
Remember that one of the rules the system uses for marking a file as purgeable is that the file must be capable of being downloaded again, whenever it is needed. So, the year-end report you’re working on using Word and Excel isn’t a candidate for being removed. That is, unless you’re keeping it in your iCloud drive, and you haven’t accessed it in a while.
Files that the system marks as purgeable and that are actually removed from your Mac are replaced with a link to the downloadable version. If you open one of the linked files, the download commences, and the file is restored.
Optimize Storage’s Contribution to Purgeable Space
macOS Sierra includes a new way to manage drive space with a technique Apple calls Optimize Storage. The idea is a simple one, and can easily free up a great deal of space on your Mac’s drives by storing some files in iCloud, and making those files available on demand to your Mac.
In a nutshell, files you haven’t used in a while are copied to iCloud for safekeeping, and then the original versions of the files on your Mac are marked by the system as purgeable. As you now know, your Mac can remove purgeable files without warning, if space is at a premium.
What’s Right and What’s Wrong With Optimize Storage
For those of us with smallish drives, such as those found in base configurations of MacBooks, MacBook Pros, or MacBook Airs, Optimize Storage can make those small, stock SSDs seem a bit larger and more usable, at least until you can upgrade them with something larger.
On the downside, for Optimize Storage to work well, you need a fast Internet connection, and a good deal of space on your iCloud drive. iCloud drive space used for Optimize Storage counts against your space allocation in iCloud. To really make productive use of Optimize Storage, you need to upgrade from the free 5 GB plan to one of the higher iCloud storage tiers, at additional cost.
Is Purgeable Space a Good Thing?
Purgeable space is the backbone of the macOS Optimize Storage feature, as well as the Store in iCloud options that let you move Desktop files, and files in your Documents folder, to your iCloud Drive, as well as move photos and videos to the iCloud Photo Library.
It really lets you do more with less, as in smaller storage devices. Of course, for purgeable space to work without being noticed, you need a fast Internet connection with no data caps or fees for bandwidth. You also need a much larger data storage plan in iCloud; finally, you need a great deal of trust that when you really, really need a purged file, it will be there for you at that very instant, and not stuck in the cloud because of congestion, bad connections, or because you’re on the road and using your iPhone’s cell plan to connect to the Internet.
Another issue is the confusion about the amount of available space on a drive. When macOS was originally released, some people had issues with trying to install Windows either in a VM or Boot Camp. The problem was that the Windows file size was larger than the available free space, but smaller than the combined free space + purgeable space. The system should have removed the purgeable space to make room for the new files, but sometimes, it wouldn’t perform the task correctly. Those types of problems should be fewer and fewer with each update to macOS, and purgeable space will become routine and trustworthy.
For myself, though, I’m keeping lots of free space on my drives. I see purgeable space as a fix that may work for Macs with limited storage space, but at the price of performance and out-of-pocket costs for iCloud storage tiers that I otherwise don’t need. I’d rather spend that money on larger local storage, either internally or externally, than keep paying monthly fees to store data in the cloud.
Over the winter holiday I updated my iMac to macOS Sierra 10.12.2. I wanted to find out if Apple had fixed any of the purgeable space issues I mentioned in this article, as well as ones brought up by our readers.
The macOS Sierra 10.12.2 update includes a number of fixes specific to managed storage and purgeable space. This includes correcting problems with Optimize Storage alerts, and improving setup and opt-out processes in iCloud Desktop and Documents.
After installing the update, I checked the purgeable space and noticed that the amount of purgeable space listed dropped from over 15 GB to under 20 MB. The bulk of the change came from items in the Downloads folder no longer being marked as purgeable. I confirmed this by downloading a couple of large files from the Apple support site, and then checking to see if the purgeable space size increased. It remained the same, indicating that when no Manage Storage options are enabled, purgeable space is being limited to just routine system files, and not any user space.
It seems macOS 10.12.2 has improved how the Manage Storage system performs, eliminating many of the concerns expressed about purgeable space.