IPhone 18 Pro Max storage can drop lower than a hard drive at 1.1 MB/s during heavy writes — QLC NAND offers…

The discovery came to light when the popular Bilibili channel Homolab published a detailed technical assessment of a 1TB iPhone 18 Pro Max. While the device handles everyday tasks, app launches, and burst data transfers with the blazing speed consumers have come to expect from Apple’s Pro-tier hardware, the testing revealed that its storage performance can drop significantly when the device is subjected to sustained heavy workloads. This performance dip is directly tied to the fundamental physics and architecture of the memory technology Apple selected for its largest capacity tiers this generation.

To understand why this performance drop occurs, it is necessary to examine the underlying technology governing modern solid-state storage. NAND flash memory stores data by trapping electrical charges in memory cells. Traditional high-performance mobile storage typically relies on Triple-Level Cell, or TLC, architecture, which stores three bits of data per individual memory cell. In contrast, QLC technology packs four bits of data into every single memory cell. This higher storage density provides a massive advantage for manufacturers aiming to cram terabytes of data into the incredibly tight confines of a modern smartphone chassis, allowing them to offer higher capacities using the exact same physical space without requiring a larger footprint inside the device.

However, this increased storage density is a double-edged sword. Packing four bits of data into a single cell requires much finer voltage control and more complex error correction algorithms than storing three bits. As a result, this higher storage density comes at the inherent cost of slower performance, particularly when the device is tasked with handling large amounts of continuous data over an extended period. When a user moves massive files, records high-bitrate video continuously, or runs intensive sustained write operations, the cache architectures designed to mask the lower native speeds of QLC memory can become saturated. Once this cache is exhausted, the storage controller must write data directly to the QLC cells, leading to a noticeable reduction in read and write speeds compared to TLC-based alternatives.

The implications of this hardware shift are particularly relevant for professional users who purchase the 1TB or future higher-capacity variants of the iPhone 18 Pro Max precisely because they rely on their mobile devices for heavy-duty content creation. Professionals often shoot hours of high-resolution ProRes video, transfer massive project files, and manage extensive media libraries directly on their phones. While brief bursts of activity will continue to benefit from Apple’s fast interfaces and high-speed controller logic, those who regularly push their phones to the absolute limit with sustained multi-gigabyte transfers may notice the effects of the QLC architecture during heavy workflows.

Apple has not formally detailed the exact breakdown of TLC versus QLC usage across the various storage tiers of the iPhone 18 Pro series, a common industry practice where component suppliers and internal memory types can vary based on capacity or manufacturing yield. However, empirical testing from independent evaluators like Homolab provides crucial insight into how these hardware choices manifest in day-to-day operations. As the iPhone 18 Pro series continues to circulate among reviewers, developers, and everyday buyers, further testing will likely shed more light on how these QLC-based NAND modules perform across different use cases and whether typical consumers will encounter these performance ceilings during normal usage.