You just spent four thousand dollars on a brand-new NVMe RAID setup, but your 8K footage is stuttering like a scratched DVD from 2004. It’s frustrating. It's actually infuriating. Most people immediately blame their RAM or their CPU, but more often than not, the bottleneck is hiding in plain sight within your storage media. This is where Blackmagic Disk Speed Test comes in, and honestly, even with all the fancy benchmarking tools we have now, it remains the gold standard for anyone touching a video file.
It’s free. It’s simple. It’s also wildly misunderstood.
Most "speed tests" give you a single number. They tell you your drive hits 7,000 MB/s and you feel great about your purchase. But that number is often a lie—or at least a very specific version of the truth that doesn't apply to professional video workflows. Blackmagic Design built this tool specifically because they knew that burst speeds don't matter when you're trying to stream 60 frames of uncompressed high-bitrate data every single second.
The Problem With Sequential vs. Sustained Speeds
Most manufacturers put "Up to 5,000 MB/s" on the box. That’s a peak. It's a sprint. It lasts for about three seconds before the controller gets hot or the cache fills up and the speed drops off a cliff.
Blackmagic Disk Speed Test is different because it uses a sustained "stress" method. It writes a large dummy file to your disk and then reads it back, over and over, while the needles on the interface bounce around. It’s mimicking the actual strain of a long day in DaVinci Resolve. If your drive can’t handle the heat—literally—the needles will start to dip. That’s the "honest" speed of your drive.
I’ve seen high-end external SSDs start at 2,800 MB/s and, within three minutes of testing, throttle down to 600 MB/s. If you’re editing a feature film, that 600 MB/s is your real speed. The 2,800 MB/s was just marketing fluff.
How to Read the Interface Without Getting Confused
When you open the app, you see two giant speedometers. Write on the left, Read on the right. Simple enough. But the real magic is the "Will It Work?" panel at the bottom.
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This isn't just a list of numbers; it's a compatibility matrix. It lists various formats—everything from standard 1080p HD to 8K DCI 60—and gives you a green checkmark or a red cross. It’s telling you, "Hey, don't even try to edit 12-bit Blackmagic RAW on this drive, you’re going to have a bad time."
The "How Fast" column next to it is even better. It tells you exactly how many frames per second (fps) your hardware can handle for specific codecs. If you see "24 fps" next to 4K60, you know you can't play back your slow-motion footage in real-time. You'll need to use proxies. It saves you the headache of wondering why your playback is choppy.
Real-World Scenarios Where This Saves Your Life
Let's talk about the "Settings" gear icon. Most people never click it.
If you click that gear, you can change the "Stress" file size. By default, it’s usually 1GB or 5GB. If you're testing a modern M.2 drive or a massive Thunderbolt 4 RAID, 1GB is useless. The drive's internal cache will swallow that 1GB file before the test even starts. You need to crank that up to 5GB to actually see what the hardware is doing.
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I remember a specific case with a local news station. They were upgrading their shared storage and couldn't figure out why their 10GbE network was lagging. We ran Blackmagic Disk Speed Test on the client machines. It turned out the server's drives were fine, but the network protocol they were using was overhead-heavy, cutting their 1,000 MB/s theoretical limit down to a measly 150 MB/s. The visual proof from the Blackmagic app ended the "he-said, she-said" between the IT department and the video editors.
Why Every Editor Needs This in Their Dock
There are plenty of other tools. CrystalDiskMark is great for PC nerds. AmorphousDiskMark is fine for Mac users who want a similar look. But they don't give you the video-centric context.
- It’s specialized: It focuses on frame rates, not just bits and bytes.
- It’s a diagnostic tool: If a checkmark turns into a red X, you know exactly which part of your workflow is broken.
- It’s a sanity check: Before you start a massive render, run the test. If your drive is almost full, speeds usually drop. It's better to know that at 9:00 AM than to find a failed render at 5:00 PM.
Keep in mind that this tool isn't perfect. It tests sequential performance—which is how video files are written—but it sucks at testing "random" performance. Random performance is what makes your OS feel fast, like opening apps or searching for files. If you're testing a boot drive to see if Windows or macOS will run snappily, Blackmagic isn't the right tool. It’s a video tool. Period.
Troubleshooting Your Results
If you’re getting lower speeds than you expected, check your cable first. Seriously. I cannot tell you how many people use a "charging" USB-C cable for a high-end SSD. Those cables are often limited to USB 2.0 speeds (about 40 MB/s). You need a cable rated for 10Gbps, 20Gbps, or Thunderbolt 4.
Secondly, check your port. Not all USB-C ports are created equal. On many laptops, only one port might be full-speed Thunderbolt, while the others are standard USB 3.2. Plug your drive into every port and run Blackmagic Disk Speed Test on each one. You might be surprised to find your "slow" drive is actually just plugged into a slow port.
Practical Steps for Optimizing Your Storage
Stop guessing. If you want a smooth editing experience, follow this workflow:
- Download the app: It’s part of the "Blackmagic Desktop Video" utility, but on Mac, you can grab it as a standalone from the App Store.
- Select your target drive: Click the gear icon, go to "Select Target Drive," and point it at your external media or RAID.
- Stress it out: Set the stress file to 5GB. Let it run for at least five full cycles. Watch if the speed drops as the drive heats up.
- Check the 10-bit and 12-bit columns: Most modern professional work is moving toward 10-bit 4:2:2. If you don't see a green checkmark under those columns for your project's resolution, start making proxies immediately.
- Audit your cables: If you aren't hitting at least 80% of the drive's advertised speed, swap the cable and re-test.
Building a reliable workstation isn't about buying the most expensive parts; it's about verifying that the parts you have are actually talking to each other at the speeds they promised. Using this tool regularly is the easiest way to ensure your hardware stays out of the way of your creativity.