A Month with Apple's Fusion Drive
by Anand Lal Shimpi on January 18, 2013 9:30 AM EST- Posted in
- Storage
- Mac
- SSDs
- Apple
- SSD Caching
- Fusion Drive
The Application Experience
By this point I’ve talked a lot about the synthetic experience with Apple’s Fusion Drive, but what about the real world user experience? In short, it’s surprisingly good. While I would describe most SSD caching implementations I’ve used as being more HDD-like than SSD-like, Apple’s Fusion Drive ends up almost half way between a HDD experience and an SSD experience.
Installing anything of reasonable size almost always goes to the SSD first, which really goes a long way towards making Fusion Drive feel SSD-like. This isn’t just true of application installs, but copying anything in general hits the SSD first. The magic number appears to be 4GB, although with a little effort you can get the Fusion Drive to start writing to the HDD after only 1 - 2GB. I used Iometer to create a sequential test file on the Fusion Drive, monitored when the file stopped writing to the SSD, stopped the process, renamed the file and started the file creation again. The screenshot below gives you a good idea of the minimum amount of space Apple will keep on the SSD for incoming writes:
You can see that if you’re quick enough you can easily drop below 2GB of writes to the SSD before the HDD takes over. I don’t know for a fact that this is the amount of free space on the SSD, but that’s likely what it is since there’s no sense in exposing a 121GB SSD and not using it all.
In most real world scenarios where you’re not aggressively trying to fill the SSD, Fusion Drive will keep at least 4GB of the SSD free. Note that when you first use a mostly empty Fusion Drive almost anything you write to the drive, of any size, will go straight to the SSD. As capacity pressure increases however, Apple’s policy shifts towards writing up to 4GB of any given file to the SSD and the remainder onto the hard drive.
I confirmed this by installing Apple's OS X developer tools as well as Xcode itself. The latter is closer to the magic 4GB crossover point, but the bulk of the application ended up on the SSD by default.
The same is true for data generated by an application. I used Xcode to build Adium, a 682MB project, and the entire compile process hit the SSD - the mechanical side of the Fusion Drive never lifted a finger. I tried building a larger project, nearly 2GB of Firefox. In this case, I did see a very short period of HDD activity but the vast majority was confined to the SSD.
I grabbed a large video file (> 10GB) I cloned over when I migrated my personal machine to the iMac and paid attention to its behavior as I copied the file to a new location. For the first 2GB of the transfer, the file streamed from the SSD and went back to the SSD. For the next 2GB of the transfer, the file was being read off of the HDD and written to the SSD. After copying around 4GB, both the source and target became the HDD instead. Fusion Drive actually ended up caching way more of that large video than I thought it would. In my opinion the right move here would be to force all large files onto the hard drive by default unless they were heavily accessed. Apple's approach does seem to be a reasonable compromise, but it's still way more aggressive at putting blocks on the SSD than I thought it would be.
I repeated the test with a different video file that I had never accessed and got a completely different result. The entire file was stored on the hard drive portion of the Fusion Drive. I repeated the test once more with my iPhoto library, which I had been accessing a bunch. To my surprise, the bulk of my iPhoto Library was on the HDD but there were a few bursts of reads to the SSD while I was copying it. In both cases, the copy target ended up being the SSD of course.
My AnandTech folder is over 32GB in size and it contains text, photos, presentations, benchmark results and pretty much everything associated with every review I’ve put together. Although this folder is very important, the truth is that the bulk of that 32GB is never really accessed all that frequently. I went to duplicate the folder and discovered that almost none of it resided on the SSD. The same was true for my 38GB Documents folder, the bulk of which, again, went unread.
Applications on the other hand were almost always on the SSD.
In general, Apple’s Fusion Drive appears to do a fairly good job of automating what I typically do manually: keeping my OS and applications on the SSD, and big media files on the HDD. About the only difference between how I manually organize my data and how Fusion Drive does it is I put my documents and AnandTech folder on my SSD by default. I don’t do this just for performance, but more for reliability. My HDD is more likely to die than my SSD.
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Galatian - Friday, January 18, 2013 - link
Thanks for pointing this out! I was very interested in getting a new iMac, as I love working on my 13" rMBP, but since I still like to game I really wanted to use the SSD on bootcamp as well. It is a huge step backward for all those people who want/need bigger SSDs. The only other option Apple offers is the 768 GB version for a whopping 1300€ upgrade price. There is no other size in between. Apple has lost me on that one.BrooksT - Friday, January 18, 2013 - link
So Apple is charging $150 to take away the headache of managing files. What you call "gouging" is what many people call "charging for a service."Death666Angel - Friday, January 18, 2013 - link
Again I have to wonder what you do with your PC. It appears as though you have no idea what is on your PC, because even saving a .doc in a specific folder is "managing files". Do you just save everything to desktop? Or download everything from the cloud and then start it from the browser download window?name99 - Friday, January 18, 2013 - link
And I wonder if you have EVER actually(a) viewed how NORMAL people use computers,
(b) used a Mac more recently than ten years ago.
Apple realized a long time ago that people has MASSIVE difficulty dealing with the file system and naming/finding files. Practically every large advance in Apple tech has been to deal with this.
iTunes and iPhoto are about dealing with "songs" and "photos", not "song files" and "photo files". Both create an environment where you never have to give a damn about where your songs and photos are stored or named in the file system. iPod follows the same path, and iOS is the logical endpoint, with no user visible file system.
And this is not new --- did you EVER expect that you should have to manually organized your email files into folders?
In OSX Apple first tried to simplify things with automatically provided folders for the most common situations (Documents, Downloads, Music, Movies, Pictures).
Now, in Mountain Lion Apple is, through a combination of different features (version storage, automatically opening apps at reboot, auto-storing files in iCloud) trying to make it so that, more and more you don't have to name documents created in apps like TextEdit. You CAN, but you don't HAVE TO.
Insisting on manually controlling the placement of your files really does start to come across as no different from insisting on writing assembly code.
Look, I'm not an idiot. I have multiple external hard drives connected to my multiple machines, and I have a purpose for the different hard drives.
The difference between you and me is that I'm not so deluded as to imagine that my needs are in any way typical, and that everyone else would be better off being forced to do things like me.
Death666Angel - Friday, January 18, 2013 - link
I see how other people use PCs. They are managing their stuff, even if they just put documents in a document folder, photos in a photo folder etc. I don't even know what not managing files would look like. Hence why I asked.I don't use Apple products.
I manually organize my Emails to folders in Thunderbird.
I also don't use the Windows libraries or the media player library or any of that stuff. I have no found a program that gave me the ability to organize "non-files" (songs, photos etc.) in a way I found easy to use, well arranged etc. I also like my files to be program/OS independent.
I don't think I'm the typical user. I never said as much.
Your last point though tells me that you don't understand the meaning of my post here. Read the other post that I did not replying to anyone. That should make it clear that I am against this technology. But if someone says he is not managing files, that just sounds dumb (real world equivalent: I don't clean up my closet and have no idea where what is).
KoolAidMan1 - Friday, January 18, 2013 - link
So many spergs in tech forums, it is unbelievable.I'm certain that most of you have low level autism and have no idea how people in the real world are.
Death666Angel - Friday, January 18, 2013 - link
I' pretty sure I'm not. What I am sure of, though, is that you are a dick. :Pkyuu - Saturday, January 19, 2013 - link
People who do the simplest management of their files (saving photos to a Photos folder, music to a Music folder, etc.) have "low-level autism"?The argument that basic file management is hard or a "headache" is absurd. It takes no time at all, and managing files and apps between an SSD and an HDD is no more difficult or time consuming than that.
KoolAidMan1 - Saturday, January 19, 2013 - link
Nope. See this is what I'm talking about.It isn't about lack of technical knowledge, it is about lack of EMPATHY.
Just because you or I or anyone around here can manually manage things doesn't mean that we should bash on automated solutions for normals. I used to write custom config.sys and batch files to get my DOS games to run properly 20 years ago, but I did it because I wanted to play the game, not because I enjoyed jumping through technical hoops.
I'm sure if you told some nerd back in 1993 that maintenance of their games from both the download service and the operating system would be the norm in 20 years, they'd bash on it for not being "hardcore" enough.
Jumping through technical hoops is nothing, you're right, its easy. It also isn't something to hold over the heads of people who don't want to go through that work.
Again, empathy, something so many insecure tech geeks are lacking when it comes to thinking about technology and products.
Galatian - Sunday, January 20, 2013 - link
Apple isn't gauging 150$. They are charging you 250€ for a 128 GB SSD! 250€ = 333$ at the current rate. Not to mention the fact, they simply don't have anything in between. It's either 128GB SSD or 766GB.I'm not sure why everybody is so apologetic about Apple on this one. They gave you much better option on last years models. They actually took options away. While I could deal with a lot of the "anti-consumer" moves that Apple has made late, this is just over the top. The new iMac is nothing more but a bigger Notebook and hence has completely lost it's value as a desktop machine.
Oh and please: How hard is it to manage files? 256 GB is fine for all my files (programs + games). Games I don't play I simply deinstall from Steam. I have a VDSL 50.000 line here, so redownloading them is a no brainer. Same goes for other programs. It must be an American problem with slow inter connections...
Also the way iPhoto handles files is extremely awkward: It actually creates a second copy of the file in another folder. That might me elegant on the surface, but I see absolutely no advantage over simply having a nice hierarchal folder structure. In fact that's what iTunes superbly does. It is a big bag of hurt, that Apple is inconsistent with the way they manage files!