Mac Fusion Drive: pro users beware

Mac Fusion Drive: pro users beware

Summary: The Mac Fusion Drive, melding SSD and hard drive, sounded like a great idea. But upon learning more this is another flashy Mac feature that won't work well for pro users, due to OS X's aging architecture.

TOPICS: Apple, Storage

My initial assessment of Apple's new Fusion Drive was positive, largely because it is the 1st hybrid drive with enough flash capacity to give users an SSD experience - but with much more capacity and at a much lower cost per GB.

But as more details emerged, I've changed my view. Fusion Drive will be good for casual users whose work does not involve processing dozens of GBs of data regularly.

But professionals in biotech, video, music, geophysical and other large data apps where availability is critical should avoid the Fusion Drive. Why?

Fusion confusion
FD is a combination of a hard drive with a 128GB SSD. The glue that holds them together is a special Mac driver that manages the movement of files between the SSD and the hard drive.

Apple's tech note says:
Fusion Drive automatically and dynamically moves frequently used files to Flash storage for quicker access, while infrequently used items move to the hard disk. As a result you'll enjoy shorter startup times, and as the system learns how you work you'll see faster application launches and quicker file access. Fusion Drive manages all this automatically in the background.

This model assumes a user who doesn't process a lot of files and whose files are small. Otherwise the bandwidth required to move files would choke the disk and the SSD capacity would be insufficient.

Users who process multi-gigabyte files regularly - musicians, video editors, scientists, artists - will find irritating starts and stops as the system is forced to move big chunks of data to accommodate new files. There is a better way.

How Seagate does hybrid
Seagate's Momentus XT hybrid algorithms take a different tack: they look for the most frequently used small files and keep them in the flash read cache. This works well because disks are good at retrieving large files, and choke on lots of small files.

Seagate marketing has been too conservative sizing the flash cache, so the SSD benefits aren't consistent for the target market. They are noticably faster, but too often revert back to standard disk performance for busy power users.

Data integrity

Fusion Drive is like Time Machine: a glitzy feature that power users turn off because it hurts performance. 

But there's a better reason for power users to avoid the Fusion Drive: data integrity. 

HFS+ is primitive 1980s file system tech. There's no background data scrubbing, checksums, or other modern data integrity features.

HFS+ assumes that writes gets written as intended and that whatever is read is what it intended - but due to many system-level issues that isn't a safe assumption. With FD your valuable files will get read and written a lot more - and face corruption every time.

The Storage Bits take
People who make a living on their Macs working with big files shouldn't risk letting HFS+ move their data around any more than they must. There will be corruption and you won't know it until it is too late. That makes FD a bad idea for pros.

Casual users will like it: it will make their Mac snappier and hide the creakiness of the aging Mach kernel. Consumers who don't have a lot of data - and most have no idea - will find themselves operating out of the SSD almost all the time and will love it.

And if they lose a file or 2? Hey, stuff happens. How often will they notice?

Comments welcome, of course. Lesson learned: act in haste, repent at leisure.


Topics: Apple, Storage

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  • Realy?

    "largely because it is the 1st hybrid drive with enough flash capacity to give users an SSD experience - but with much more capacity and at a much lower cost per GB."

    Realy this is 1st HD with enough flash capacity? What about RevoDrive?:
    And when apple announce price for FD, they must if you telling as "much lower cost per GB"...

    Apple’s price on a 256GB SSD for $300 so we can expect that the FD will be 2/3x more expensive than its equivalent... typical.
    • edit

      should be:
      Apple’s price on 256GB SSD is $300, is just 2x the going rate of an equivalent product on NewEgg...
    • Apple Gouges on SSD prices

      I don't know where you get that $300 for a 256GB SSD figure from. But as I've detailed elsewhere, Apple gouges customers for SSD storage:


      Yep, Apple gouges on their other products as well.

      EG, if you want to purchase a Macbook Air laptop with a 256GB Solid State Drive instead of the standard 128 GB, it will cost you $300 extra as an upgrade for the additional 128GB; that's $2.34/GB.

      You can buy the latest generation Samsung 256GB drive, the same company from which Apple buys the chips for their drives, for $170 retail; that's $0.66/GB.

      That's more than 3.5 times the cost! Plus, Apple is paying less than wholesale to Samsung.

      Given the fact that you can only get this upgrade via Apple (with the inconvenient exception of warranty voiding upgrades), it IS gouging.

      @James Katt: your premium product argument is flawed. These are essentially identical commodity memory chips. We're not talking Ford vs. Ferrari here.

      The Apple drive only comes with a 90 day standard warranty. The Samsung drive comes with a 3 year warranty. "Premium" in this case means basically identical, much more expensive, and less warranted.

  • Too much hypothesys

    First, your claims that Seagate's firmware moves small files etc is absolutely bogus, as no hard drive can have any idea about "files", ever! What it does is basically use the SSD as an extension of the RAM cache, that's about it.

    There is no danger of any sort for your files, as they get moved. Exactly the opposite, any rewrite of a file reduces the chance for consequent bad read and losing data.

    I find this article absurd. It does not talk at all about what professionals care: performance.
    Do you have any hard facts about the FD performance vs any other HDD, or not?
    Throwing out FUD just to see some smart responses is not very professional...

    By the way, anyone concerned about the safe storage of their data will store them on networked ZFS volume, and nothing else.
    • And..

      And "will find irritating starts and stops as the system is forced to move big chunks of data..."

      How do you know? Have you a week's worth of actual time on one of the drives to confirm this? I doubt it. Why in the world would a journalist / engineer ever assume something like this?

      You don't know if this will actually happen, or if Apple built a scheduling algorithm so that files are only moved during low levels of system use.

      While HFS+ maybe aging, let's base our stories on tested facts, please.
  • And you know this from personel experience with the Fusion drive tech?

    I wouldn't offer opinions, one way or the other, until I've had extensive hands on experience with the tech.

    Just saying, Robin.
  • Yea seriously...

    Apple should leave the Big Boy products to the Big Boys. There are enough ignorant people that will buy anything that pops out of the Bauble Factory and believe that it is actually a great, innovative and magical product.

    Fortunately I think the "pro" people mentioned in this blog will be better clued in.
    • Coming form the person who can't spell "yeah"

  • Not the full story

    All the user feedback of the Segate combo drives has been not very good performance. And the bandwidth issue is not real, there is more than enough bandwidth on SATA 3 to support the movement of data between the SSD and Disk without any issues. The side of the SSD is fine for most applications and can be increased by Apple or thorough 3rd party drivers. There is info today about creating Fusion Drives on Mac Pro's with Apple software, so you can have a Fusion drive with as big an SSD as you can afford.

    The issue of data integrity on HFS+ is real from a technical stand point but not for a practical one, professional in the Audio and VIdeo community have been using HFS+ for a very long time without any issues of reliability, in fact from the large audio video facilities I worked with, experience MUCH greater reliability with OSX based HFS+ than modern windows files systems. There is not question that Apple will need to improve HFS+ in the future but to suggest it is not reliable as compared to anything else practical for use as a workstation is not accurate.
  • Guesses and out of date info

    You were ether basing this off of your own assumptions or on early speculation from other users. You assume facts that are not in evidence.

    1) You have no idea wether this system does a data integrity check or not as part of the house keeping.
    2) You don't know if this process is file or block based (indications now are block based). Which would change the frequency with which data was moved.

    There is every indication that this feature is outside of HFS+ and will work on ZFS or even NTFS and other drive formats. If you want to argue that people should not trust HFS+ we can have that debate but you don't know enough about how Apple is doing this yet....nobody does.
  • Completely Wrong

    Fusion drive re-organizes blocks only during times when io requests are quiet. Yes, it's block level and doesn't operate during user activity.
    Jack Zahran
  • Informed Analysis

    BYO Fusion Drive

    The blog referenced by Ars:
  • You need all the details to make an opinion

    Before you make wild ass opinions and conclusions, you need to understand all of the details. Check out this link.

    The fusion drive is much more than just a caching system. It works at the block level and not the file level. It also only moves data when the IO system is idle so that its work does not interfere with normal read/write requests. The is OS level support for this system.
  • Open foot insert mouth.

    Robbin Harris, you have lost all credibility. You write an opinion piece on something you know nothing about, and present it as fact. Next time you decide you're going to review a piece of technology, at minimum you should have tested said technology and had your facts straight.
  • Well then I don't want to be a "power" user ;)

    "Fusion Drive is like Time Machine: a glitzy feature that power users turn off because it hurts performance."

    Sure Robin. I'm sure Dr. Bertrand Serlet [the man directly responsible for Time Machine] can't wait to hear from you. LMAO.