Why Reviewers Test Sequential Writes and Mixed Workloads

Hardware reviewers test both sustained sequential writes and mixed workloads to provide a complete, accurate picture of a storage drive's true performance. While manufacturers often advertise peak speeds based on short bursts of simple data transfers, these numbers rarely reflect everyday use. Sustained sequential write tests push hardware to its limits to expose cache sizes, thermal throttling, and true base speeds during heavy tasks like transferring massive video files. Conversely, mixed workload tests simulate real-world daily computing—such as gaming, running an operating system, and multitasking—where the hardware must read and write data simultaneously. Testing both ensures consumers know how a drive performs under both extreme stress and normal, everyday conditions.

The Purpose of Sustained Sequential Write Tests

Sequential writes involve transferring large, continuous blocks of data to a drive, such as copying a 100GB movie file. Manufacturers love to advertise sequential speeds because they produce the highest numbers. However, they usually only measure these speeds in short bursts.

Reviewers use sustained sequential write tests to see what happens when a drive is forced to write massive amounts of data continuously. This exposes three critical factors:

• Cache Exhaustion: Most modern Solid State Drives (SSDs) use a small portion of super-fast memory (often called an SLC cache) to absorb incoming data quickly. Once this cache fills up during a large file transfer, write speeds can plummet—sometimes to levels slower than a traditional mechanical hard drive. Sustained testing reveals how big this cache is and how slow the drive gets once it runs out.
• True NAND Speed: After the cache is full, the drive must write directly to its main storage blocks. Sustained tests show the actual, unassisted speed of the storage media.
• Thermal Throttling: Writing data continuously generates significant heat. If a drive gets too hot, it intentionally slows itself down to prevent damage. A sustained test shows if the hardware's cooling solution can handle heavy, prolonged work.

The Purpose of Mixed Workload Tests

In everyday computing, a storage drive rarely just reads or just writes data in a neat, continuous line. Instead, it constantly jumps around, reading and writing small files at the exact same time. This is a mixed workload.

When you boot up your computer, launch a game, or browse the web, your system might be reading application files while simultaneously writing temporary cache files, system logs, and background updates. Reviewers typically test this using a 70% read and 30% write ratio to mimic real-world usage.

Mixed workload testing is vital because:

• It Exposes Controller Weaknesses: The controller is the "brain" of the storage drive. Reading and writing require different electrical voltages and processes. Some controllers are terrible at switching between reading and writing quickly, causing the system to stutter or freeze, even if the drive has high advertised speeds.
• It Measures Real-World Responsiveness: How fast your computer "feels" depends heavily on how well it handles mixed workloads. A drive that excels here will load applications faster and handle multitasking smoothly.

Why Both Tests Are Necessary

Relying on just one of these tests leaves a blind spot.

If a reviewer only tests sustained sequential writes, they might recommend a drive that is great for a video editor moving massive files, but feels sluggish for a casual user running multiple office programs.

If a reviewer only tests mixed workloads, a consumer might buy a drive that feels snappy during web browsing, only to find out it slows to a crawl the moment they try to back up their photo library or install a massive game.

By testing both sustained sequential writes and mixed workloads, reviewers strip away marketing gimmicks and show exactly how hardware will behave in both worst-case stress scenarios and typical daily use.