Blackmagic Disk Speed Test: How to Use It and What the Results Mean

Why This Tool Matters for Video Editors

Video editing is one of the few tasks where storage speed directly affects whether your workflow is usable. If your drive can’t read footage fast enough, you get dropped frames, stuttering playback, and failed exports. Blackmagic Disk Speed Test (free, macOS only) is the standard tool for checking whether a drive can handle specific video formats and frame rates. It’s simple, fast, and tells you exactly what you need to know.

Running the Test

  1. Download Blackmagic Disk Speed Test from the Mac App Store (free)
  2. Open the app
  3. Select the target drive from the dropdown (it defaults to your startup disk — change it if you’re testing an external drive)
  4. Click the Start button (the big play icon)
  5. Wait 30-60 seconds for the test to complete

The test writes and reads a large block of data to the selected drive and measures the sustained throughput in MB/s. It runs multiple passes and shows both the write speed and read speed.

Reading the Results

The main display shows two numbers: Write and Read speeds in MB/s. Below the speed numbers, there’s a table showing which video formats the drive can handle at those speeds. Green checkmarks mean the drive is fast enough; red X marks mean it isn’t.

The table covers common video formats: ProRes, DNxHR, H.264, H.265 at various resolutions (HD, 2K, 4K, 8K) and frame rates (24, 25, 30, 50, 60 fps). If you’re editing 4K ProRes 422 at 60fps and the table shows a green checkmark, your drive is fast enough. If it shows a red X, you’ll have playback problems.

What Speeds Do You Actually Need?

Some reference points for common workflows:

  • 1080p H.264 editing: Any modern SSD handles this. 100 MB/s read is plenty.
  • 4K ProRes 422: Needs roughly 300-400 MB/s sustained read for smooth playback at 30fps.
  • 4K ProRes 4444 or 8K: Needs 500+ MB/s. Only NVMe SSDs and RAID arrays handle this.
  • 6K+ RAW (RED, Blackmagic RAW): Needs 800+ MB/s. Fast NVMe RAID or direct-attached SSD arrays.

Mechanical hard drives typically hit 100-200 MB/s. SATA SSDs hit 500-550 MB/s. NVMe SSDs hit 1,000-7,000 MB/s depending on the drive and interface. The speed test tells you what your specific drive actually delivers under sustained load, which is different from the peak speeds advertised on the box.

Common Mistakes

  • Testing the wrong drive: Make sure you selected the correct drive in the dropdown. Testing your Mac’s internal SSD when you want to know about your external drive is useless.
  • Testing an almost-full drive: SSDs slow down significantly when they’re nearly full (less space for wear leveling). Test with at least 20% free space for accurate results.
  • Testing over a slow connection: An NVMe drive in a USB 3.0 enclosure is limited to ~400 MB/s by the USB bus. The drive might be fast, but the connection isn’t. Use Thunderbolt or USB 4 for external NVMe drives.
  • One test isn’t enough: Run the test 2-3 times. SSD performance can vary between runs, especially on drives with thermal throttling.