What's so special about Apple's new Fusion Drive?
By	Geoff Duncan	@geoffduncan — Posted on	October 29, 2012 4:01PM PST 10.29.12 - 4:01PM PST
When Apple announced its updated iMac and Mac mini desktop computer models last week, it also took the wraps off a new storage technology called a Fusion Drive. The Fusion Drive is supposed to combine the high performance and low power requirements of a flash-based solid-state drive (SSD) with the sheer storage capacity of a traditional hard drive — but implemented so users never need worry about what data and applications happen to be on each kind of storage.
Is the Fusion Drive a genuine step forward in computer storage, or is it just a slick rebranding of so-called hybrid drives that've been combining SSD and traditional hard drive technologies in notebooks for a couple years?
What is the Fusion Drive?
As announced last week, Apple's Fusion Drive essentially combines a 128GB flash-based SSD drive with either a 1TB or 3TB 3.5-inch traditional hard drive. Although this combination is a new drive configuration from Apple, it's not unprecedented in the PC industry. For several years, PCs have been available with multiple drives, and it's been pretty common for high-end notebook and desktop users to opt for machines that have a small SSD for their operating system and key apps that require high speed access but large-capacity hard drives for things like photos, movies, video, and music.
However, Apple has taken the idea one step further. Those PCs with both an SSD and standard hard drive treat those drives as separate devices. For Windows users, the SSD is typically the C: drive, and the traditional hard drives (or their partitions) appear as separate drive letters. Apple is taking a different approach with OS X Mountain Lion. The SSD drive and the hard disk that comprise the Fusion Drive appear as a single logical volume. So far as the user is concerned, there's just one hard drive, and they never have to worry about distinguishing between the computer's flash-based storage and hard drive storage.
The intelligence to manage the flash and hard drive storage is built into OS X Mountain Lion. Mountain Lion will automatically keep the operating system and a user's key applications in the flash portion of the Fusion drive for best performance. Apple notes that the entire OS X operating system and all the apps that ship with it will fit into the 128GB of flash storage with room to spare. However, the prioritization doesn't stop there. Mountain Lion keeps tabs on applications and data most frequently accessed by the user (often called "hot" data), and prioritizes it for storage on flash media. Less frequently-used (or never-used) data gets shuffled off to the hard drive for long term storage. The result is that users never have to worry about how to manage data across the two storage mediums. "It just works," noted Phil Schiller, Apple's senior vice president of worldwide marketing, at Apple's keynote last week.
Isn't a Fusion Drive the same as a hybrid drive?
Apple's Fusion Drive sounds like a so-called "hybrid drive," which aim to boost the performance of traditional hard drives by building in some additional flash-based storage. The best-known hybrid drives are the Momentus XT line, intended for notebook computers; but there are also products like the PCI-based RevoDrives from OCZ Technologies that are aimed towards the desktop markets.
Apple's Fusion Drive differs from hybrid drives in two primary ways. First, Apple is using more flash storage by packing 128GB of flash, an amount which will likely increase as Apple revises and upgrades the offering. Conversely, Seagate's Momentus XT drives only incorporate 4GB to 8GB of flash storage. OCZ's RevoDrive line is more directly comparable to the Fusion Drive — it packs 100GB of flash storage.
Second, and more importantly, hybrid drives use their flash storage merely as cache. All hard drives pack a bit of RAM memory to speed up read and write operations; it's not unusual these days for hard drives to pack 8MB to 32MB of RAM to boost performance. Hybrid drives essentially just treat their built-in flash storage as an extension of this cache. The most recently-accessed "hottest" data is stored in flash first, essentially on its way to and from the hard drive without much (or any) consideration for the nature of that data. Conversely, Apple prioritizes the use of flash storage to things like files, programs, and data that are most likely to boost performance — and the user never needs to worry about managing it.
Another distinction is that Apple isn't making Fusion Drives available in its notebook line where systems like the MacBook Air and Retina MacBook Pros rely solely on non-upgradable, soldered-on RAM and flash storage. The Fusion Drives are desktop-only.
How the Fusion Drive will work in Macs
The Fusion Drives are brand new, so we don't have much information on how they will work. However, Apple has posted a Knowledge Base article that clarifies a few things.
First, Fusion Drives have to be pre-installed in a Mac. You can't get an iMac or a Mac mini with an SSD drive, attach an external hard drive via Thunderbolt or Firewire, then use Disk Utility or another program to have the Mac treat the combination as a Fusion Drive. Inside the Mac, the Fusion Drive will exist as two physically separate storage devices, but users won't be able to roll their own Fusion Drives using off-the-shelf pieces.
However, if users so desire, they will be able to partition off part of a Fusion Drive's hard disk as a separate volume. This can be very handy to creative professionals and other people who tend to work on large sets of data (say, raw video or an immense image set), and then archive off the project when they're done. With a separate partition, the workspace can be wiped out and reformatted in one simple step, and users dont' have to worry about fragmentation and other issues impacting performance down the road. However, the Fusion Drive is limited to just one of these extra partitions, and that partition doesn't get any performance boost from the flash portion of the Fusion Drive.
How much of a performance boost can users expect? Apple characterizes performance of flash-based storage as about 3.5 times faster than a traditional hard drive. According to Apple, desktop Macs equipped with a Fusion Drive will boot twice as fast as a hard drive-equipped model, perform tasks like importing photos into Aperture as much as 3.6 times faster than a traditional hard drive, and copy files 3.7 times faster. However, Apple does note that users might experience hiccups if they over-run the Fusion Drive's flash storage — including dropped frames during massive video imports, for example.
Downsides of the Fusion Drive
So are there downsides to Fusion Drives? As with all storage technologies, they do have their compromises.
Windows — Users who dual-boot their Macs between Mac OS X and a version of Windows using Boot Camp will be pleased to know they can create a separate partition on a Fusion Drive, and use that partition for Boot Camp. There are a couple gotchas, though. That's only supported on the 1TB Fusion Drives for now, and the Windows partition won't get any performance boost from the flash portion of the Fusion Drive. Remember: the brains behind the operation are baked into OS X Mountain Lion, not the drives themselves.
Access from other systems — Fusion Drives can be shared over a network just like any other logical volume. What's more, they can be mounted directly on another system using Target Disk mode — but only so long as the other system is running OS X Mountain Lion 10.8.2 or later. Previous versions of Mountain Lion (or Lion, or Snow Leopard, etc.) don't know how to deal with Fusion Drives.
Maintenance and troubleshooting — Apple does offer a special version of Disk Utility with Mountain Lion that can handle Fusion Drives available in the Internet version of Mountain Lion Recovery. So, if a Fusion Drive has problems, users aren't totally out of luck. However, third-party disk repair utilities, like Alsoft's DiskWarrior, will need to be updated to handle Fusion Drives.
Upgrades or third-party Fusion Drives? — Although Fusion Drives seem to rely on more-or-less standard SSD sticks and 3.5-inch hard drives, there's no word yet on whether either of those components can be upgraded and still keep a Mac's "Fusion Drive" capabilities. Hitachi already makes 4TB 3.5-inch hard drives, and drive makers are continuing to push the limits of storage technology. No one is going to be surprised if 6TB 3.5-inch drives are available in a few years. Or maybe you want to boost your Mac's performance even further from 128GB of flash to 256GB or more — can it be done? (That is, assuming you have the technical chops to get inside Apple's new desktop systems.) Nobody knows yet…but don't be surprised if the answer is no.
Similarly, we don't know yet if anyone else will be allowed to make Fusion Drives. In theory, the new Macs' Thunderbolt port has more than enough bandwidth to boot and see significant performance increases when used with a hypothetical external Fusion Drive — but don't expect Apple to offer one. There's also no indication yet if Mac storage vendors like La Cie will be able to offer external Fusion Drive solutions.
Cost — Finally, Fusion Drives aren't cheap. Although Apple's new iMacs won't be available until next month, configuration information for the new Mac mini indicates a 1TB is a $250 upcharge from a standard 1TB drive running at 5,400 rpm. That's kinda pricey since 128GB SSDs currently range from about $100 to $175. Apple is charging a premium for the Fusion Drive — and right now, it doesn't look like there's any other way to get one. It's a bit reminiscent of the outrageous prices Apple charges for RAM: 8GB of RAM for a Mac mini is $100 from Apple — more than twice what third-party vendors charge for the same upgrade.
All in all, it's very tempting to describe Apple's Fusion Drive as what hybrid drives should have been all along. Sure, people have been packin both SSDs and traditional hard drives into their computers for a few years and getting substantial performance benefits. But there's always been an unfortunate and awkward overhead of having to manually manage what applications and data are on which drives, and many SSD drives designed to improve startup times are as small as 20GB — barely enough to hold an operating system, let alone a user's critical apps and files. With the Fusion Drive, Apple includes enough SSD storage for meaningful performance benefits with even demanding apps and data — and takes the headaches out of managing the separate storage media. In a few years, we may find ourselves wondering why we ever managed SSD and hard drive storage any other way.
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