If you have been working in macOS Sierra for a while you may have seen something called “Purgeable Space.” The first time I saw this I said, “what the heck is purgeable space?”. It is no big deal really, unless you have limited storage space on your Mac.
What IS Considered Purgeable Space
Here is a pretty good definition of 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.
OK, that is a lot of stuff. In all my research on Purgeable Space I have determined you really cannot TELL the OS what to make Purgeable or not. It is setup to decide on it’s own. However, here is the bottomline with Purgeable Space. It is designed to work with the Optimize Storage feature in macOS Sierra. Here is a whole article on my blog on Optimize Storage.
How To View Purgeable Space
If you wish to see how much “Purgeable Space” is on your HD, go under the Apple Menu and select “About This Mac:”
About This Mac opens in the “Overview” tab. Just click on “Storage” and your hard drives will be displayed. It may take a minute for your hard drives to finish drawing. When they do, About This Mac shows you the basic makeup of stuff on your HD. If you hold your mouse over the last segment in the bar, Purgeable Space will be displayed. In my case, it is 7.6 GB large.
Another way to see this is to open the Disk Utility app and do the same thing. It will show you Purgeable Space:
You don’t have to hold your mouse over it, Purgeable Space is just displayed along with “Used” and “Free.” One more thing before we move on here. The highlighted area in the bottom of the Disk Utility window shows Available Space. It calculates that as Purgeable + Free Space. Why is that important? If you are doing a Get Info command to determine available space on your HD in macOS Sierra, you get what Disk Utility refers to as Available. That can be a little misleading because it is counting Purgeable Space as Available when theoretically it is not Available.
Here is the bottomline with all this. If you have limited space on your HD, maybe you are using a laptop, then you might wish to use Optimize Storage which then uses the Purgeable Space feature. Just be sure to read the definition of Purgeable Space in the section above first to see what may be purged. You will need a fairly good sized iCloud Storage setup to use the Optimize Storage feature as well. The iCloud Drive Storage is not cheap. As far as I am concerned, I would prefer to use the money from iCloud on an external HD and just leave Optimize Storage completely off. I guess I just don’t trust it to remove stuff from my machine on it’s own. It is a neat idea and may work for some, but it is not my ‘cup of tea.’
If you need HD space you may wish to turn Optimize Storage on and use the Purgeable Space feature. On the other hand, if you have plenty of HD storage I would not bother with it. Actually, I wish there was a way to turn off Purgeable Space to regain that HD real estate, but as far as I can see that is not possible.