Tests conducted by the Bilibili tech channel Homolab revealed that the 1TB version of the iPhone 18 Pro Max exhibits significant storage performance drops under sustained high-load conditions. While the 512GB model maintains consistent speeds, the 1TB variant experiences a sharp decline in write performance once its SLC cache is exhausted.
The performance gap is attributed to the use of QLC flash memory in the 1TB model, which stores four bits per cell compared to the three bits in TLC flash. While QLC enables higher storage density, it is inherently slower and less durable during complex write and erase operations.
In Q1T1 sequential tests, the 1TB model scored 8168 points, trailing the 512GB version's 11285 points by approximately 38%. Under continuous heavy write stress, the 1TB model's average write speed dropped to 79.4 MB/s, with some instances falling as low as 25.6 MB/s.
Apple utilizes an SLC cache to mitigate these limitations, allowing speeds of up to 3000 MB/s during normal usage. Analysts note that this performance degradation is unlikely to affect average users, as it only triggers during extreme, sustained data-intensive tasks that exceed the cache capacity.
Professional users who frequently handle large ProRes video files or perform massive data migrations may be more impacted by these architectural trade-offs. The findings highlight the ongoing industry challenge of balancing storage capacity, cost, and performance in mobile devices.
