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Explaining Sierra’s Optimized Storage

One of the marquee features of macOS 10.12 Sierra is Optimized Storage, a marketing term that Apple’s SVP of Software Engineering Craig Federighi introduced during the Worldwide Developer Conference in June (see “macOS 10.12 Sierra to Succeed OS X 10.11 El Capitan,” 13 June 2016). He described Optimized Storage as having two core functions, making room for new files by keeping old ones in the cloud and getting rid of files you’ll never need again.

Federighi claimed that Apple took a representative Mac with 20 GB free on a 250 GB drive and “turned on all the switches” to clean out another 130 GB of space. For those struggling to free up space, particularly on a notebook Mac with relatively little internal flash storage,
Optimized Storage sounded great, at least if you don’t mind paying for online storage in iCloud Drive. And while it could be a great boon for such people, it turns out to be a somewhat confusing collection of seemingly unrelated features, burdened by one of the stranger interfaces that Apple has produced in recent years.

Plus, although we haven’t had time to test all the possibilities, I recommend care when it comes to Optimized Storage in general, and extreme caution with one of its settings. That isn’t to say you shouldn’t enable all its features, but that you should understand the possible implications before doing so.

Accessing Storage Management — Before I get into the specifics of what comprises Optimized Storage, since you won’t find that exact term anywhere in Sierra’s user interface, let’s look at how you access it. Choose  > About This Mac, and click the Storage button. You’ll see a stacked bar graph for each of your drives showing how much data of each type is on each drive — the categories include items like Apps, Documents, GarageBand, iBooks, iCloud Drive, iOS Files, Mail, System, Photos, and Other. At the end of the chart, you may see a hashed area that Sierra labels as Purgeable. Apple doesn’t clarify what’s included in Purgeable, but I suspect it
comprises things like logs, cache files, and the contents of the Trash. Also new in this window is a Manage button.

Click Manage to bring up the centralized dashboard for Optimized Storage. In a truly odd interface decision, Apple chose to let you turn on Optimized Storage features from within the System Information app, rather than a pane of System Preferences, where nearly every other system-level setting resides. You can also bring up this window directly within System Information by choosing Window > Storage Management. The main thing to realize about the Storage Management window is that it’s more of an
assistant than a control panel — you can enable Optimized Storage’s settings here, but what you see depends on what other settings you’ve selected, and you can’t turn off or adjust any settings here. You do that in completely different parts of Sierra’s interface.

Managing Files Manually — The Storage Management window presents a familiar interface with a left-hand sidebar and large pane on the right that changes based on what you select in the sidebar. The top item, Recommendations, is where the most interesting stuff happens, and I’ll explain its contents in a moment. But first, notice all the other entries in the sidebar, which correspond to the blocks of color in the About This Mac dialog’s Storage view. For some app-based items, like GarageBand, Mail, and Photos, the Storage Management window merely gives you a button to open the app so you can manage its contents from within the app itself.

For a few app-based items like iBooks, and folder-based items like Applications, Documents, iOS Files, and Trash, Storage Management instead provides a Finder-like list view that shows each file’s name, size, and last accessed date, along with kind for apps and documents. Click the column headers to change the sort, so you can focus on versions of similarly named files, see which files you haven’t touched in years, or just look at them sorted by size.

Hover over any item and you see an X button for deleting the file and a magnifying glass button that reveals the file in the Finder. With these tools, Apple is trying to make it easier for you to delete large files you no longer need. You don’t need to delete files one by one, either — just Command-click or Shift-click to select multiple files and press the Delete key to remove them all at once. You’re given the combined size of all the selected files and warned before they’re deleted, so you can
use this technique to preview how much space a multi-file deletion will save.

The Documents view of Storage Management has three sub-views that help you focus on the task of clearing out unnecessary files, starting with the largest:

  • Large Files, which on my MacBook Air lists files larger than 50 MB

  • Downloads, which shows the contents of the Downloads folder

  • File Browser, which provides a column view that’s sorted by folder size and shows file sizes as well

Other nice touches abound. In the Applications item, the Kind column shows you which apps came from the Mac App Store, which didn’t, and which are older versions or duplicates that you can probably delete. I was surprised to find nearly 1.4 GB of old and duplicate apps on my MacBook Air. Notice too that different screens have different buttons, so Applications has a button to open the associated folder and Trash has an Empty Trash button. One thing you won’t find is a graphical view like what GrandPerspective provides; nonetheless, I suspect that Apple’s Storage Management interface will put a significant dent in the demand for utilities like CleanMyMac and Onyx.

But let’s move on to the meat of Optimized Storage, as represented by the sections in Recommendations view: Store in iCloud, Optimize Storage, Empty Trash Automatically, and Reduce Clutter. I’ll explain these in order of increasing complexity. Note that the wording (and even the icons) in this section changes depending on what options you may have already set. I’ve even seen it change multiple times as I’m watching, which is a horrible user experience. If it doesn’t reflect what you believe it should, quit and relaunch System Information, open the Storage Management window again, and let it sit for a few minutes.

Reduce Clutter — I hesitate even to give this section a subhead since it’s merely interface sleight of hand. All clicking the Review Files button here does is switch you to the Documents view so you can sort through and remove unnecessary files manually, as I discussed above.

Empty Trash Automatically — Moving up, the next section is Empty Trash Automatically, which is easy to understand. As it says, once a file has moldered in the Trash for 30 days, the Finder deletes it automatically, much like Photos automatically removes unwanted photos in its Recently Deleted folder after 40 days. Before this, files accumulated in the Trash until you emptied it manually, even if you ran out of drive space. I don’t yet know if Sierra’s Finder will offer to empty the Trash if you run very low on space.

Amusingly, Microsoft Windows has been capable of automatically deleting files from its Recycle Bin at least since Windows 98, although back then it deleted older files when adding a newer file to the Recycle Bin caused it to exceed a user-specified size. I’m surprised it took Apple this long to get to the point of taking the trash out for the user.

Whether or not you choose to enable this setting depends on what sort of person you are. If you can’t stand the concept of wasting space — even space you don’t need — on the contents of the Trash, you’re probably emptying it manually all the time now. Automatic deletion of trashed items after 30 days likely won’t scratch that itch for you. However, if you, like me, almost never empty the Trash unless you start to run low on drive space, I recommend turning on Empty Trash Automatically to help keep your Mac’s drive from getting too full. It’s a bad idea to let your drive fill up since that can cause crashes, corrupted files, and even directory corruption.

This setting also appears in Finder > Preferences > Advanced as the “Remove items from the Trash after 30 days” checkbox.


Should you ever wish to turn it off, you’ll need to do that in the Finder Preferences, since enabling it in the Storage Management window replaces the Turn On button with a green Completed checkmark icon.

Optimize Storage — Now we’re getting into the confusing bits, starting with the fact that this aspect of Optimized Storage is called Optimize Storage (notice the missing “d”?). Clicking the Optimize button provides two options, one to automatically remove watched movies and TV shows and another to keep either only recent email attachments or no email attachments.

Although I haven’t been able to verify this for certain, I believe the Optimize Storage button affects only movies and TV shows purchased from the iTunes Store. When enabled, iTunes deletes watched movies and TV shows automatically, which is likely a good way to save a lot of space quickly, given the size of most video files.

Again, the Storage Management window of System Information only allows you to enable the Optimize Storage feature. To enable it directly within iTunes, or to turn it off if you want to make sure you can hold onto an already watched movie or TV show, go to iTunes > Preferences > Advanced, where you’ll find a checkbox called “Automatically delete watched movies and TV shows.”

Of course, you can always retrieve a deleted video in iTunes by choosing Movies or TV Shows from the Media Picker, clicking the Library button in the navigation bar, and clicking the Download button that looks like a cloud with an arrow coming out of it.

In an earlier incarnation of this article, I said that the email attachment feature had been removed in a late beta. That was wrong; the Storage Management window initially failed to present it to me, and to others, as an option, but after tweaking the feature in Mail manually, it returned. To find that setting, open Mail > Preferences > Accounts > acccount-name > Account Information. There’s a pop-up menu for Download Attachments that can be set to All, Recently, or None. The Optimize button in Storage Management gives you the choice of setting that menu to Recently or None for all your accounts; once set there, you can change it only in Mail’s preferences.

There isn’t that much new here; Mail has long had the option to not download attachments automatically (the Recently option is new). When you read a message with an attachment that’s not downloaded, you can click its icon in the message to retrieve it. Apple hasn’t said at what point Mail will consider an attachment no longer “recent,” but I presume that it will at some point delete older attachments from the local mail archive such that you’d need to retrieve them again from the server.

Store in iCloud — The most confusing aspect of Optimized Storage comes in the first section of the Storage Management window, which is called Store In iCloud. The controls available in this section encapsulate two entirely separate features in Sierra, and worse, even the wording and checkboxes change depending on what you’ve already done.

On a Mac that doesn’t have iCloud Photo Library enabled, when you click Store In iCloud, you get a dialog that gives you two checkboxes, one that lets you turn on syncing for your Desktop and Documents folders and another that enables you to turn on iCloud Photo Library. If either of those features is already on, the dialog changes (in the second dialog, I have iCloud Photo Library enabled, so it focuses on Desktop and Documents folder syncing).

At this point, I need to explain Desktop and Documents folder syncing, a new feature in Sierra that’s only peripherally associated with Optimized Storage. When enabled via the Storage Management window of System Information or the master switch at System Preferences >
iCloud > iCloud Drive > Options, this feature moves your Desktop and Documents folders from your home folder to iCloud Drive (itself a chimerical folder/volume). Don’t look for them in your home folder because they’re gone — I can’t imagine why Apple didn’t make symbolic or hard links to them in the spot where every user has been trained to look for them for the last 16 years. You can still access them from the sidebar in Finder windows, from the Finder’s Go menu, or from within iCloud Drive.

The beauty of Desktop and Documents folder syncing is that as you enable it on other Macs using the same iCloud account, the contents of those folders on other Macs are merged via iCloud, so you end up with a single unified folder for Desktop and another for Documents. Even better, you can access the full contents of those folders via the iCloud Drive app on any iOS device signed in to the same iCloud account. It works well from what we’ve seen, but it may take some getting used to for those who have long maintained very different systems. I’m looking forward to using it to transfer screenshots made on one Mac to another automatically, since the Mac saves screenshots to the Desktop.

I have two warnings surrounding Desktop and Documents folder syncing. First, if you have gigabytes of data in one or both of these folders, you may have to start paying, or pay more, for storage space on iCloud Drive. The first 5 GB is free, and after that Apple offers several tiers from 50 GB to 2 TB. The storage space is shared with iCloud Photo Library, so if you’re already paying for more to sync photos, you may have enough. But if you are going to start paying, it might be worth getting enough to use both Desktop and Documents folder syncing and iCloud Photo Library.

My second warning is that turning off Desktop and Documents folder syncing is stressful. When you do this, in System Preferences > iCloud > iCloud Drive > Options, Sierra tells you that all your files will be available only in iCloud, which seems wrong: if you’re turning off syncing, you’re doing so because you want them locally. However, that dialog is followed immediately by another that tells you that you can recover your files from iCloud Drive.

In fact, what happens when you turn off that feature is that Sierra recreates empty Desktop and Documents folders in your home folder. You can’t replace those, so you can’t drag the old Desktop and Documents folders from iCloud Drive to your home folder; instead, you must open each folder in iCloud Drive and move (Command-drag) its contents to the local Desktop and Documents folders in your home folder. You can try to delete the now-empty Desktop and Documents folders from iCloud Drive, but in my
experience, iCloud keeps recreating at least the Desktop folder.

In general, if you ever turn off an iCloud Drive feature and seem to be missing files, restart your Mac and wait a bit. You can also check for the files on itself.

Trust in iCloud? — Now that you understand Desktop and Documents folder syncing, we can return to what happens when you enable the checkboxes that you get in the Storage Management window when you click Store In iCloud. The effect of clicking these checkboxes goes beyond just turning on Desktop and Documents folder syncing and iCloud Photo Library, and this is where Optimized Storage comes in again:

  • With Desktop and Documents folder syncing, when you open System Preferences > iCloud > iCloud Drive > Options, there’s a checkbox called Optimize Mac Storage. When selected, it allows Sierra to delete old, large files from your local drive to save space, leaving just a copy in iCloud Drive — you’ll still see the icon in your Finder, but it will have a cloud badge on it, indicating that it’s not stored locally. If that gives you the willies, you’re not alone.

    The question here revolves around backup. Let’s say you turn on this feature, and it copies the contents of your Desktop and Documents folder to iCloud Drive. Time passes, and some old, large files in your Documents folder are deleted from the local drive to free up space. They still exist in iCloud Drive, appear on your local drive as stubs that you can click to download, and in any local backups created before they disappeared from your local drive. Now imagine that your backup drive dies, and you need to
    create a new backup. Will those old, large files be downloaded from iCloud Drive and backed up? Or will the version in iCloud Drive be the only extant copy?

    I cannot currently recommend selecting this Optimize Mac Storage checkbox. It will take time to test what happens with backup strategies when Optimized Storage starts deleting files, and since you presumably have sufficient space on your Mac now, it’s better to be safe than sorry.

  • With iCloud Photo Library, selecting the checkbox in Store in iCloud also selects an Optimize Mac Storage radio button in Photos > Preferences > iCloud. That has the effect of storing full-resolution photos and videos in iCloud and only keeping them on the Mac if there’s space. (When you work with an item whose full-resolution original is in iCloud, Photos downloads it first.)

    There’s nothing new about this iCloud Photo Library setting; it has been in Photos since the launch of iCloud Photo Library. In the past, however, you had to enable Optimize Mac Storage manually, and we have firmly recommended that you never enable it on your primary Mac, where you presumably have sufficient drive space for your entire photo library. Optimize Mac Storage is great for a MacBook Air that lacks room for all your photos, but in our view, you should always have a full local copy of
    all your photos, backed up on local storage.

In the end, the question comes down to whether or not you trust iCloud, because once you enable these features, iCloud becomes the “truth,” in the lingo of syncing. That’s fine if you have local copies and local backups to restore from should something horrible happen to iCloud or your account, but in both of these cases, it seems theoretically possible that you could end up with no local copies at all. If you’re not all that attached to your data, or if you’re willing to cede all responsibility for your data to Apple, that may be acceptable. Personally, I want to know that I have a copy of every document and photo stored locally on at least one Mac and backed up locally in at least one spot.

During WWDC, Craig Federighi said that Apple has over 10 billion documents in iCloud today, although I wonder if that number includes photos or reflects mostly iOS storage, given how few people I see using iCloud Drive to store Mac documents. The problem is that I’ve heard too many stories about people experiencing problems with data stored in iCloud to trust it implicitly. I’m not perturbed about iCloud security in particular; Apple makes all the right noises about iCloud security and privacy. But there’s a big difference between having the right intentions and eliminating all bugs. iCloud is usually fine as a syncing service, but that’s a far stretch from trusting it with
the only copy of valuable data.

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