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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  • A5 - Monday, October 07, 2013 - link

    Not really, no. They're at about the same level of abstraction since they both sit above the driver stack. Reply
  • Flunk - Monday, October 07, 2013 - link

    There is also the issue that the driver sits farther up the stack than it does in Windows. Mach being a hybrid microkernel and all. I'm sure they can close the gap with a lot of work, but it doesn't erase the fact that Mac OS's basic structure is not designed to provide direct hardware access. Reply
  • overzealot - Monday, October 07, 2013 - link

    The Windows kernel is also a hybrid microkernel. Reply
  • bestham - Monday, October 07, 2013 - link

    "Storage & Fusion Drive – By default all of the iMacs come with a 3.5” mechanical hard drive." The physical harddrive size is differentiated between the 21.5" and the 27". I suspect that you already knew this but it slipped. Reply
  • Anand Lal Shimpi - Monday, October 07, 2013 - link

    Thank you, fixed :) Reply
  • rootheday3 - Monday, October 07, 2013 - link

    My opinion: Many games look pretty good at medium and it is not clear that the compromise in frame rate is worth it to push for higher settings vs running at medium with higher resolution.

    Regarding the Iris Pro gaming results - the jump from 13x7 medium (where Iris seems to have plenty of power to spare) up to 16x9 high/very high - this is a change of two variables: both resolution and settings.

    Can you rerun some of the gaming tests at 16x9 medium (or maybe native panel resolution - 19x10 medium where 13x7 results were close to 60fps) to see what that shows?
    Reply
  • rootheday3 - Monday, October 07, 2013 - link

    one other question - is there any ability to OC the IGP in the bios? Typically Intel gpus have a fair bit of OC headroom and it would be interesting to see:
    1) what kind of performance/playability can be extracted
    2) to what extent the igp clock frequency is the limiter on Iris Pro vs cpu, memory bandwidth, etc.
    Reply
  • jeffkibuule - Monday, October 07, 2013 - link

    This is a Mac! There is no bios, never has been. Reply
  • DanNeely - Monday, October 07, 2013 - link

    Everyone who isn't an annoying pedant conflates bios and uefi in general usage. Reply
  • repoman27 - Monday, October 07, 2013 - link

    And everyone who isn't an annoying pedant would also realize that jeffkibuule meant, "There is no [user accessible BIOS/EFI/UEFI], never has been." Reply

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