Storage & Fusion Drive

By default all of the iMacs come with a 2.5" or 3.5” (21.5/27" iMac) mechanical hard drive. It’s been quite a while since I’ve forced myself to use a system with only a HDD, and going back to one now just reaffirms what I’ve been thinking for a while: HDD-only systems have been killing the PC industry for a while now. The experience just isn’t great. OS X continues to do a great job caching frequently used data in main memory, something the iMac has plenty of in its default 8GB configuration, so the HDD-only option does quickly become bearable. However, shooting for bearable is aiming too low in my opinion.

The iMac is an unusual member of Apple’s Mac lineup in that it is one of the only systems to ship with a HDD by default. Both the MacBook Air and MacBook Pro with Retina Display are SSD-only, and the same will be true for the coming Mac Pro. My guess is that Apple views the iMac as targeting a slightly different audience than those systems, an audience more used to large, single-volume storage.

Long term I believe Apple has a solution to this problem other than forcing everyone to accept a two-volume approach to storage (or, alternatively, dealing with small/fast local storage and putting everything else in the cloud). That solution is Fusion Drive.

I went through a deep analysis of Apple’s Fusion Drive with the 2012 iMac, so I’ll spare you the details here. At a high level, Fusion Drive is a software managed SSD “caching” solution on top of a 128GB SSD and 1TB or 3TB HDD. I put caching in quotes because Fusion Drive doesn’t actually act like a cache but rather a software managed, spanned storage volume. Fusion Drive appears as a single volume equal to the capacity of SSD + HDD, with the software layer intelligently managing what data ends up on the SSD and what ends up on the HDD. Fusion Drive is similar to what you’d do manually if you had a small SSD and large HDD in a single system. You’d put frequently used applications on the SSD and relegate everything else to the HDD. The difference is that Fusion Drive can manage storage on a block level, whereas you’re only able to move data between drives at a file/application level. In theory, if you had a workload that could fit entirely on the 128GB SSD, Fusion Drive would be indistinguishable from a user managed SSD + HDD setup.

In real world testing, Apple’s Fusion Drive continues to be the closest approximation to an SSD experience from a hybrid setup that I’ve tested. The reason why is quite simple: Apple’s Fusion Drive comes with sufficient NAND to cache the overwhelming majority of IO. While most hybrid setups use somewhere between 8GB and 32GB of NAND, Fusion Drive only has a single option: 128GB. I’m a bit disappointed that Apple didn’t increase that to 256GB with this most recent upgrade to the iMac, but my 128GB/1TB Fusion Drive configuration has been great for the past year. It’ll be interesting to see whether Apple eventually moves to a 256GB SSD component or if it instead makes Fusion Drive a standard option on next year’s iMacs as NAND prices drop.

My personal preference is still for a large SSD that I manage myself, combined with a large external HDD array (perhaps over Thunderbolt), but if you need a single storage volume, Fusion Drive is absolutely the way to go. I remember writing a similar line back during my initial evaluation of the Fusion Drive but thinking to myself: there can’t be that many people who really fall into this category. It turns out I was wrong.

Over the past year I’ve also had a fairly regular argument with a friend of mine who was researching computer options for his sister and brother-in-law. They are both Mac users and I kept steering him towards a 13-inch MacBook Pro with Retina Display, but he kept pushing back saying that they needed at least 1TB of storage and it had to be inside the system as a single volume. No amount of reasoning had any affect, both individuals ended up with 13-inch MacBook Pros, complete with hard drives. I’m more of the force users to adopt sort of person, but I do understand that old habits die hard for many.

Fusion Drive is of course still offered on both of the new iMacs and it’s $50 cheaper than it was at the 2012 iMac introduction. Fusion Drive should honestly be a minimum requirement for anyone buying one of these systems. I understand why Apple still offers mechanical storage as the default configuration for both iMac models, but to anyone considering either - you’ll want to at least spring for the Fusion Drive upgrade.

Doing so brings the price of the entry level 21.5-inch iMac up to $1499, the same price it would be if you opted for a 256GB SSD instead. Either option is fine, just make sure you choose one of them - even if the target user for the system is someone else. For years I’ve gone into detail as to why solid state storage is better than traditional HDDs, so I won’t go into any depth here. The experience really is night and day, and it’s honestly a must-have for any modern computer.

GPU Performance: Iris Pro in the Wild The Display


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  • rootheday3 - Monday, October 7, 2013 - link

    I don't think this is true. See the die shots here:

    I count 8 different die configurations.

    Note that the reduction in LLC (CPU L3) on Iris Pro may be because some of the LLC is used to hold tag data for the 128MB of eDRAM. Mainstream Intel CPUs have 2MB of LLC per CPU core, so the die has 8MB of LLC natively. The i7-4770R has all 8MB enabled but 2MB for eDRAM tag ram leaving 6MB for the CPU/GPU to use directly as cache (how it is reported on the spec sheet). The i5s generally have 6MB natively (for either die recovery and/or segmentation reasons) but if 2MB is used for eLLC tag ram, that leaves 4 for direct cache usage.

    Given that you get 128MB of eDRAM in exchange for the 2MB LLC consumed as tag ram, seems like a fair trade.
  • name99 - Monday, October 7, 2013 - link

    HT adds a pretty consistent 25% performance boost across an extremely wide variety of benchmarks. 50% is an unrealistic value.

    And, for the love of god, please stop with this faux-naive "I do not understand why Intel does ..." crap.
    If you do understand the reason, you are wasting everyone's time with your lament.
    If you don't understand the reason, go read a fscking book. Price discrimination (and the consequences thereof INCLUDING lower prices at the low end) are hardly deep secret mysteries.

    (And the same holds for the "Why oh why do Apple charge so much for RAM upgrades or flash upgrades" crowd. You're welcome to say that you do not believe the extra cost is worth the extra value to YOU --- but don't pretend there's some deep unresolved mystery here that only you have the wit to notice and bring to our attention; AND on't pretend that your particular cost/benefit tradeoff represents the entire world.

    And heck, let's be equal opportunity here --- the Windows crowd have their own version of this particular fool, telling us how unfair it is that Windows Super Premium Plus Live Home edition is priced at $30 more than Windows Ultra Extra Pro Family edition.

    I imagine there are the equivalent versions of these people complaining about how unfair Amazon S3 pricing is, or the cost of extra Google storage. Always with this same "I do not understand why these companies behave exactly like economic theory predicts; and they try to make a profit in the bargain" idiocy.)
  • tipoo - Monday, October 7, 2013 - link

    Wow, the gaming performance gap between OSX and Windows hasn't narrowed at all. I had hoped, two major OS releases after the Snow Leopard article, it would have gotten better. Reply
  • tipoo - Monday, October 7, 2013 - link

    I wonder if AMD will support OSX with Mantle? Reply
  • Flunk - Monday, October 7, 2013 - link

    Likely not, I don't think they're shipping GCN chips in any Apple products right now. Reply
  • AlValentyn - Monday, October 7, 2013 - link

    Look up Mavericks, it supports OpenGL4.1, while Mountain Lion is still at 3.2

    Good overall improvements in the Developer Previews alone.
  • tipoo - Monday, October 7, 2013 - link

    ML supports a higher OpenGL spec than Snow Leopard, but that doesn't seem to have helped lessen the real world performance gap. Reply
  • Sm0kes - Tuesday, October 8, 2013 - link

    Got a link with real numbers? Reply
  • Hrel - Monday, October 7, 2013 - link

    The charts show the Iris Pro take a pretty hefty hit any time you increase quality settings. HOWEVER, you're also increasing resolution. I'd be interested to see what happens when you increase resolution but leave detail settings at low-med.

    In other words, is the bottleneck the processing power of the GPU (I think it is) or the memory bandwidth? I suspect we could run Mass Effect or something similar at 1080p with medium settings.
  • Kevin G - Monday, October 7, 2013 - link

    "OS X doesn’t seem to acknowledge Crystalwell’s presence, but it’s definitely there and operational (you can tell by looking at the GPU performance results)."

    I bet OS X does but not in the GUI. Type the following in terminal:

    sysctl -a hw.

    There should be line about the CPU's full cache hierarchy among other cache information.

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