Update: Apple subsequently fixed the issue. I’m unsure exactly which update did so, but everything is fine again in macOS 10.12.4. One thing to note if you have more than one Mac: when you switch on iCloud drive, all of the files and folders that were on your desktop will be moved to a Desktop folder inside iCloud Drive – see Apple’s support document on this. Documents from your other Mac(s) will be found inside a folder with the same name as the Mac.

I wrote an opinion piece last month entitled macOS Sierra’s new storage-management tools are a bit of a mess

Effectively you are switching from a belt-and-braces system, where you have three copies – one local, a second in your local Time Machine backup, a third on iCloud – to just a single copy. That’s way too risky for my tastes, especially given the somewhat flakey reliability record of Apple’s cloud services.

But Mac users may also be running that same risk without even realizing it. Because that first option – to ‘Optimize Mac Storage’ for files stored on iCloud – is on by default in my experience. This means that, for any file on iCloud, your Mac could be deleting files from your Mac without your knowledge or permission. That should never be the case.

I was wrong. Sierra’s storage-management aren’t a ‘bit of a mess’ at all: having just seen what they did to my MacBook Air, seemingly prompted by the update to 10.12.1, they are a complete and utter disaster … 


I have two Macs. My main machine is my heavily-upgraded 17-inch MacBook Pro. That has 2TB of SSD storage, My MacBook Air is my portable writing machine, used mostly in coffee shops. I don’t keep many documents on it, so I was using well under 100GB of its 256GB SSD.

Optimize Mac Storage was switched off on both machines. But it appears that Sierra doesn’t just switch it on by default when you first upgrade – it also switches it back on again when you do a dot update. As before, there is no warning that it has done so.

The first point at which I became aware of the fact was when I sat down to enjoy a cup of Earl Grey in a coffee shop and work on my SF book: my MacBook Air immediately complained that its SSD was full. “What the … ?” I asked myself. I checked.


Sure enough, iCloud Drive had completely filled up my SSD. It did this so thoroughly that I couldn’t even take this screenshot initially, as it told me there was no room to do so.

I clicked to see the size of the drive. 162GB.


At this point, I was essentially forced to use the Optimize option to try to get my drive back. So, reluctantly, I clicked the button. Bear in mind here, too, that I was sitting on the usual rubbish coffee-shop wifi, so this wasn’t a fast process.

By the end of it, there was a whole lot of bad news.

First, it deleted almost all my documents; it left me with just a handful. Not the most recently-opened ones, as you’d expect, but completely random ones. By this point, I again couldn’t take screengrabs, so had to take photos of the screen for the next part of the adventure.

There very briefly seemed some good news, as it was now showing an iCloud Drive with less than 1GB in it:


So, this should have solved my problem. But no, I still had less than 1GB of free drive space. How? I took a look at Storage again:


So despite iCloud Drive now being empty, all the documents from it were still somewhere on my machine. In the Documents folder, right? So I went to see what was in the Documents folder. Almost nothing. I did a File Info on the Documents folder to see:


Nope, not there. So where were all these documents? I went to the top level of the drive and sorted the folders by folder size. The Mac failed to calculate their sizes in that view, but doing a File Info on each in turn revealed no large folders at all.

I opened Disk Utility, and it agreed that the drive was full. I remembered a trick to purge data: switch Time Machine automatic backups off then do a restart. I did that. Still no difference.

Repeating the whole optimizing routine and restarting yet again changed nothing. AirDrop wasn’t playing, so I decided to email myself the two screengrabs I’d got before the drive was too full even for those. Uh …


Yes, one of the files Sierra had deleted was my mailbox profile (I use Postbox rather than Apple Mail). So I couldn’t even open the app! I tried some other apps. Some opened, others couldn’t, either because Sierra had deleted needed files or because there was not enough drive space to create the temporary files needed to open the app.

Effectively, Sierra had turned my MacBook Air into a useless hunk of aluminum. It was bricked.

That wasn’t all …

A few minutes later, an unpleasant thought occurred to me. On my MacBook Pro, my entire Documents folder sits inside my Dropbox folder. That allows me to get access to any document I might need from any device anywhere. On the MacBook Air, I use a selective folder sync so that I sync only my active writing folders. Those documents are not stored on iCloud – yet optimizing storage removed them all from my Air.

Sierra just zapped all my active writing folders, and – as they are inside a Dropbox folder – that would tell Dropbox to delete them too. My MacBook Pro, sitting on my home WiFi some 30 miles away would then dutifully delete them from my primary Mac also.

I paused Dropbox syncing to stop this wholesale carnage, but sure enough, this morning I got an alert from Dropbox:


As a techie, this was a nuisance rather than a disaster. I have multiple backups, and I knew that Dropbox would let me undelete the files. For me, it’ll be a few hours of my life lost to a tedious task. But a non-techie could have just lost everything.

As far as that evening’s writing was concerned, it was over. As Sierra had deleted the local copy and I’d switched Dropbox off, I no longer had a copy of the book to work on.

Well, actually I did. Being a true belt, braces and piece of string man where data is concerned, I keep a tiny USB drive permanently plugged into my MacBook Air, and I use a son-father-grandfather system to keep copies of the last three versions. So a copy of the latest Scrivener file was sat on the USB key, but … I didn’t have enough space on my Mac to copy it across.

I could have worked directly on the USB key, but I didn’t want to risk a crash when it ran out of drive space completely. I did at least manage to use the time usefully by writing this instead, which required nothing more than a web browser.

I’m not alone in this kind of experience. Here are some excerpts from the comments on my previous piece.

I have just had a really nasty experience – and a confusing one to boot. I have only got the standard 5Gb iCloud storage and yet the system reported that my iCloud drive contained 169Gb. That worried me for a start. Next problem – everything started running very slowly. Disc access was dreadful, beachballs all the time. When I moved files from the Desktop – where I keep a lot of stuff – and links to My Documents – there was a cloud icon next to everything in Folder Details view. Also, when I tried to move files the system asked me if I ‘Really wanted to remove files from iCloud’. I had no intention or desire – and I thought utterly no storage space to put all my files in the cloud and I certainly didn’t think I had done so. So, I turned it off. I lost all my desktop settings and all My Documents.

I’m just having the same experience […] I just went to turn off the iCloud drive because all my Document files had a cloud icon on the side (that I don’t remember turning on btw ), and the only way to accept the “turning off” was deleting all my documents and desktop folders???? 

This seems really badly done. You can only select documents and desktop and it deletes everything instead of files you never use. 

It looks to me like Apple not only failed to consider the needs of those who don’t spend their lives on always-on, high-speed broadband; not only neglected to think about the dangers of robbing people of backup copies of their work; but also hasn’t even considered that many of us have more than one Mac with different sized SSDs on each. And instead of failing gracefully in that situation, it bricks the Mac. That’s utterly nuts.

As far as I can see, the only reliable way out of this mess is going to be to completely wipe the drive and restore from Time Machine. And then immediately unlink my MacBook Air from iCloud so that the same thing doesn’t happen again. In other words, remove it from the Apple ecosystem that is half the reason I’m a Mac guy in the first place! Crazy!

So yeah, I was wrong. There is no ‘bit of mess’ about this: the word I would use to describe it begins with ‘cluster’ and ends with a four-letter word I can’t use on a family-friendly site. Apple very badly needs to fix it.


Some commenters were skeptical that Sierra could switch on the cloud storage features by default or without prompting. I’m highlighting comments from others who have experienced the same thing. I’m not doubting that Sierra shouldn’t do this, but the reality is that for some people it does. What variable determines this behaviour isn’t yet known.

Optimize storage *was* turned on on my Mac, though I never turned it on. I think the option to move Docs and Desktop to iCloud Drive was on too although I never turned it on either.

Thanks for posting this. I had “optimise storage” turned off and just checked. Yep, it had been changed to turned on with 10.12.1 without me knowing.

Thanks for this pointer. I just checked and Sierra had switched on Optimize Storage again on both my iMac and my Macbook Pro.

Same here. Very unsatisfactory.

I most definitely did not turn on “optimise storage” when I was prompted after the Sierra install. However, it turned itself on on both of my macs.

It has also been suggested that storing the Dropbox folder inside the Documents folder is unwise. Based on this experience, I would agree (and have now moved it), but note that this is in fact the default location for a Dropbox folder, and this has been the case since long before Sierra, so it’s something Apple should have known.

A Time Machine restore has solved the problem. For now, I am staying logged-out of iCloud on the machine.