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Content Delivery Summit [1 June 2020]
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Streaming Media West [19-20 Nov 2019]
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Video Engineering Summit [19-20 Nov 2019]
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Sourcing High-Speed Storage for Mac Pro 4K Editors

If you're making the jump to 4K editing and find yourself needing a jolt of capacity and speed, don't expect external SSD drives to come close to the performance of internal drives on your Mac Pro (or most computers). Read on for some alternative solutions.

So you bought a new Mac Pro for video editing, lured by its unique combination of raw power and small form factor. Thinking ahead, you bought the maximum 1 TB of storage, thinking it would be sufficient for most projects, which you could save off to slower, external storage for archiving. Now a longer, 4K project has come through, and you need fast extra storage for project files and the like.

If you’re like me, one of the first things you did after setting up the Mac Pro was to test the speed of its internal SSD drive, which is truly phenomenal. I did when I received the Mac Pro I rented from VFX Technologies for a recent consulting project. I downloaded the Blackmagic Design Disk Speed Test, and saw the awe inspiring results shown in Figure 1 (below).

Figure 1. The inspiring Write/Read performance of the internal SSD drive on the Mac Pro.

My project absolutely needed an external drive. Knowing that the Thunderbolt connection is much faster than even the speed shown in Figure 1, I thought that a Thunderbolt-based SSD drive would duplicate the results of the Mac’s internal drive. So I bought a 1GB Transcend StoreJet 500 Portable SSD drive for $565 at Amazon.

Do the math, and you get a cost per GB of $565, highlighting that cost is the major downside of SSD. Like anything else, however, sometimes you have to pay for speed, and I was willing. Then I pointed Disk Speed Test at the drive, only to see the discouraging results shown in Figure 2 (below).

Figure 2. The depressing performance statistics on the Transcend external Thunderbolt drive.

It’s All About Connections

What gives? An SSD is an SSD, right? Well, yes and no. An SSD drive is an SSD drive, but the connection to the drive controls performance. On the Mac Pro, the connection to the internal drive is via PCI Express (PCI) bus, which basically is the same connection as the slots in a desktop computer that you plug graphics and other peripheral cards into. Interestingly, it’s also the same technology used in Thunderbolt, which is why Thunderbolt is so fast.

What about the connection to the external drive? Well, that’s obviously via Thunderbolt, but the technology controlling the external drive is SATA, the same technology that controls most traditional drives. And that’s the bottleneck, or at least the major component of it.

Want proof? Figure 3 (below) shows the Mac’s Disk Utility report from the two drives. On top is the Macintosh HD, connected via PCI. On the bottom is the Transcend drive, connected via the much slower SATA connection.

Figure 3. Mystery solved. The internal drive connects via PCI, the external via SATA.

The Cliff Notes version is that PCI is much faster than SATA, so the Mac’s internal drive is much faster than external drives controlled via SATA. If you’d like to learn more about the differences, there’s a great article on Overclock entitled SSD Interface Comparison: PCI Express vs. SATA.