Final Words

For the first time since late 2008, I went back to using a machine where a hard drive was a part of my primary storage - and I didn’t hate it. Apple’s Fusion Drive is probably the best hybrid SSD/HDD solution I’ve ever used, and it didn’t take rocket science to get here. All it took was combining a good SSD controller (Samsung’s PM830), with a large amount of NAND (128GB) and some very aggressive/intelligent software (Apple’s Core Storage LVM). Fusion Drive may not be fundamentally new, but it’s certainly the right way to do hybrid storage if you’re going to do it.

It seems that Fusion Drive is really made for the user who doesn't necessarily have a ton of applications/data, but does have a reasonable sized media collection. For that user, Fusion Drive should be a reasonable approximation of a well managed SSD/HDD setup with your big media files going to the HDD and everything that you launch frequently living on the SSD. I’m always going to ask for a larger cache, but I do believe that 128GB is a good size for most client workloads and usage models today. For me in particular I’d probably need a 256GB cache for Fusion Drive to win me over, but I understand that I’m not necessarily the target market here.

The real question is whether or not it’s worth it. I’m personally a much bigger fan of going all solid state and manually segmenting your large media files onto HDD arrays, but perhaps that’s me being set in my ways (or just me being right, not sure which one). Fusion Drive doesn’t do anything to mitigate the likelihood that a hard drive will likely fail sooner than a good SSD, whereas if you go with an internal SSD and external (Thunderbolt or USB 3.0) HDD RAID array you can control your destiny a bit better. Unfortunately, in situations where Fusion Drive is a choice, you don’t often have that flexibility.

On the iMac, Apple limits your options quite a bit. You can either buy a hard drive or the Fusion Drive on the 21.5-inch model, there’s no standalone SSD option. There the choice is a no-brainer. If you’re not going to buy your own SSD and replace the internal HDD with it (or try to see if OWC’s rMBP SSD fits), then the Fusion Drive is absolutely right choice. You’re paying handsomely for the right ($250 for 128GB of NAND is very 2011), but if you’re not willing to crack open the iMac case this is really the only way to go.

For the 27-inch iMac the decision is similarly difficult. Apple does offer a standalone SSD option, but it’s for a 768GB model that will set you back $1300. All of the sudden that $250 Fusion Drive upgrade sounds a lot more reasonable.

On the Mac mini side the decision is far simpler. The Fusion Drive is only available on the $799 configuration (for $250) but so is a 256GB SSD upgrade for $300. As long as you’re ok with using an external hard drive for mass storage, here I’d go for the big standalone SSD. The usual caveat applies: this  is only true if you’re not interested in cracking open the mini yourself and using a 3rd party SSD.

To make things simpler, I made bold the options I'd choose given Apple's current lineup in the table below. Note that this is still assuming you're not going down the DIY route (if you do go down that path, buy the biggest SSD you can find and rely on some external mass storage for everything else):

Fusion Drive Options
  Mac mini (2012) 21.5-inch iMac (2012) 27-inch iMac (2012)
Base System Cost $799 $1299/$1499 $1799/$1999
1TB Fusion Drive +$250 +$250 +$250
3TB Fusion Drive - - +$400
Largest Standalone SSD 256GB
- 768GB

I am curious to see how long of a roadmap Fusion Drive has ahead of it. Will NAND get cheap/large enough that even the iMac can move to it exclusively? Or will we end up with systems that have more than enough NAND to easily store everything but large media files for even the most demanding of power users? In less than a year Apple could double the size of the NAND used in Fusion Drive at no real change to cost. I suspect another doubling beyond that would be necessary to really make Fusion Drive a one size fits all, but then we're talking ~2 years out at this point and I don't know how static everyone's usage models will remain over that period of time. Go out even further in time, to the post-NAND era and there are some really revolutionary things that can happen to the memory hierarchy altogether...

Fusion Drive Performance & Practical Limits


View All Comments

  • Hrel - Friday, January 18, 2013 - link

    Those entire folders wouldn't go on the NAND, they'd go on the HDD. Read the article on here about the MomentusXT from Seagate. Reply
  • Hrel - Friday, January 18, 2013 - link

    found it for you Reply
  • name99 - Friday, January 18, 2013 - link

    Yeah, and USING Momentus XT sucks. The experience is horribly uneven.
    Enough stuff comes up fast that you get used to that, but enough stuff comes up slowly that it's REALLY noticeable because you're used to the occasional bursts of speed.

    I've used Momentus, I've used Fusion. There is no comparison.

    In fact (true story) after I replaced the broken HD in a friend's MacBook Pro with a Momentus she told me a week later that she thought the computer was still broken because it seemed to behave so strangely, sometimes feeling really fast, then a little later feeling so slow.

    Now, if Momentus were kitted out with
    - 64GB (maybe even just 32GB) of
    - FAST flash (not the cheap crap used in USB thumb drives) AND
    - cached writes
    it might work well. But that's not the product that Seagate is selling.
  • Death666Angel - Friday, January 18, 2013 - link

    2 of your 3 points are very correct. But they do use SLC which is not the cheap stuff. Reply
  • name99 - Friday, January 18, 2013 - link

    If they do use decent flash, then why don't they cache writes?

    I always assumed it was because their flash (like USB thumb flash) was so crappy that it was slower for random writes than the HD was.
  • kyuu - Saturday, January 19, 2013 - link

    Because there's a lot more to it than just using the right NAND. Also, for the 2nd-gen Momentus XT they were going to release a firmware update that would enable write caching. I'm not sure if that ever happened, haven't followed up on it recently. Reply
  • kyuu - Saturday, January 19, 2013 - link

    That's because the MacBook/MacOS sucks. Not the Momentus XT's fault.

    Been using a Momentus XT in a Windows machine for a long time, had no problems with it being "uneven".

    Also, they sure as hell don't use cheap flash "used in USB thumb drives".
  • ShieTar - Saturday, January 19, 2013 - link

    How would the HDD know what is a file? The OS will just command a drive to write a given data block to Sector X.

    The drive may treat X as a logical address, and reorder data internally, but it has no clue if it is writing a complete file or parts of it, or just writing zeros as ordered by some secure erase software.
  • Subyman - Friday, January 18, 2013 - link

    Any word on how much the migration process increases read/write quantity over a manually managed setup? As for ssd life being longer than hdd life, if we take into account that almost all writes will hit the ssd first and then some will transfer to the hdd this means the hdd is accessed less often. This could level the mean read/write to failure rate to make the hdd even with the ssd, unless migration has an effect that I'm not considering. Reply
  • dimmer - Friday, January 18, 2013 - link

    Did you enable TRIM or not? Reply

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