Roll Your Own Fusion Drive: Benchmarks

fusion_drive_iconApple’s new so-called Fusion Drive technology is interesting.  The cost of SSD drives is falling but not at a rate that consumers (or apparently Apple) would like.  To that end, Apple engineers have come up with a novel solution that is proving to be a surprisingly effective middle-ground initiative.  A Fusion Drive is comprised of two separate drive mechanisms.  The first is an SSD drive 128GB or greater.  The second drive is a conventional spinning hard drive, either 5400rpm or 7200rpm, now typically referred to as an HDD.  The HDD can be pretty much any size, currently all the way up to 3TB.

What turns these two disparate drives into a Fusion Drive is the way they’re formatted.  Apple’s Core Storage API includes the ability to effectively stripe the two drives into a single logical volume.  Think of the single volume as a hybrid: the best parts of SSD (fast, fast, fast) with the best parts of the HDD (lots of cheap space).  But what makes the Fusion Drive truly remarkable is what happens to the data on the drive automatically and invisibly once formatting is complete.  Once the SSD and the HDD have been merged into a single Fusion Drive, the Mac OS becomes responsible for distributing the data across the two separate drive mechanisms.  It does this allocation with intelligence.   The most used data files, or files that benefit most from faster access times are stored on the SSD.  Larger or lesser used files are stored on the HDD’s spinning platters.  The idea being that the files on the SSD can be accessed more quickly, having vastly superior read and write times.

Following the same logic, the Fusion Drive stores the entire operating system on the SSD.  This ensures the Mac will boot quickly.  If you’re used to booting from a conventional hard drive (HDD), watching your Mac boot from a Fusion Drive will be a sobering experience.  We’re talking fast!  But if you’re accustomed to seeing your machine boot from an SSD, what should you expect?  How does the performance of a Fusion Drive based Mac compare to a strictly SSD based Mac?  I did some benchmarks to be sure, but the short answer is that most of the time you can’t tell the difference!  Expect your SSD based Mac to boot in just about the same amount of time as a Fusion Drive based Mac.

After I merged the two drives in my MacBook Pro into a Fusion Drive, I ran a benchmark.  Then I compared it to a benchmark I ran on the lone SSD when I first installed it in the same MacBook Pro back in mid 2012.  Oddly, in most tests, the Fusion Drive actually scored higher than the lone SSD drive.  Honestly, I wasn’t expecting that.

Here are the raw benchmarks.

MacBook Pro SSD Only:

SSD Bench in Optical Bay 1

SSD Bench in Optical Bay 2

SSD Bench in Optical Bay 3

MacBook Pro Fusion Drive (240GB SSD 500GB HDD):

Fusion Drive Test 1

Fusion Drive Test 2

Fusion Drive Test 3

Not only did the Fusion Drive perform impressively, but for some reason it out performed the purely SSD based configuration at times.  I’m not clear on the cause.  I anticipated a possible performance loss to the Fusion Drive configuration, minimal at best.  But the numbers don’t lie.  For what its worth, I’m testing on an Early 2011 15″ MacBook Pro with a 240GB SSD and a 500GB 5400rpm HDD.  Nothing exotic.  The current test of the Fusion Drive was run on a freshly installed and fully updated version of Mac OS X 10.8.3.  The solo SSD test goes back to August 2012 but the OS was a clean install and fully updated at that time as well.  It would’ve been a slightly older version of the OS back in 2012, but not drastically different.

My overal take on this configuration is simple.  The Fusion Drive is impressive.  Under normal circumstances that OS does an impressive job of allocating the disk space and moving the files to keep disk access fast and efficient.  Based on what I’ve read, files of 4GB or larger might start to exceed the range of the OS’s ability to optimize them to the SSD.  At this point it is still unclear if that 4GB barrier might change based on the size of the SSD used in the Fusion Drive.  For example, Apple’s configurations use 128GB SSD’s and those tests reflected the 4GB barrier.  But since I used a 240GB SSD in my configuration, might I get something closer to 6GB or 8GB of data before performance drops back to customary HDD speeds?  It would be nice but it’s too soon to tell.  I’ll be taking a closer look.  But, for right now, it’s enough to know that the Fusion Drive configuration is a solid performer.

Lastly, lets take a moment for a vital word of warning.  As with any computer configuration, always backup your data.  This mantra becomes more critical when using a Fusion Drive configuration.  Why?  You have to keep in mind that the operating system is dynamically allocating data across two physical discs.  This happens on a constant basis.  And a Fusion Drive offers no data redundancy.   This means that if either drive suffers a hardware failure all of the data will be lost.  Look at it this way: you’ve doubled the number of drives needed for your computer to operate.  You’ve vastly improved performance but you’ve doubled the chances of hardware failure.  Is it likely to happen?  Absolutely!  It’s only ever a matter of time.  Will it happen soon?  Probably not.  But now is a great time to take advantage of the Mac’s built-in backup feature, Time Machine!  Protect your data… before it’s too late!

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