The author of the Bilibili channel HOMOLAB tested the most expensive version of the iPhone 18 Pro Max with a 1TB storage drive. The test results were disappointing: it turned out that the manufacturer noticeably cut costs on this particular component of the smartphone.
Unlike the lower-end modifications with TLC memory, the 1TB version of the iPhone 18 Pro Max uses QLC chips. This type of cell allows for higher data storage density but is inferior to TLC in speed and endurance.
When reading in 4KB blocks, the difference between the different types of storage was small: TLC cells were 11.37% faster. However, in mixed read and write operations, the gap was already between 12% and 38%, depending on the usage scenario.
The difference was most noticeable during prolonged sequential writing. While the fast SLC cache is available, the speed exceeds 3000 MB/s. After it fills up, writing switches to an additional buffer operating in a mode close to TLC — here the average is 578 MB/s.
When this resource is also exhausted, data begins to be written directly to QLC: the speed then drops to an average of 79.4 MB/s, and at times to 25.6 MB/s (this is lower than many budget microSD cards).
When 60% of the memory is occupied, the available SLC cache shrinks from about 250GB to 58GB, and the average speed of the intermediate buffer drops from 578 to 396 MB/s. Direct writing to QLC under such conditions averages 45 MB/s, at times slowing to 1.1 MB/s.
For short operations, the drive manages to work through the fast cache, and the maximum speed drop occurs during prolonged writing of large amounts of data. Such scenarios include long video recording (4K or ProRes), saving large files, and restoring from a backup.