iPhone 18 Pro Max storage speed can crawl to a near standstill when you push the 1TB model hard enough. New benchmark tests show the drive falling well below typical flagship speeds under extreme, sustained write loads.
The slowdown traces back to a storage swap Apple made to fit more gigabytes on the same chip in its most expensive models.
iPhone 18 Pro Max storage speed bottleneck slows 1TB model
Apple markets the iPhone 18 Pro as a godsend for professional creators and calls it “purpose-built for unprecedented performance.” But the iPhone 18 Pro Max’s biggest storage options apparently come with a catch: The more you push them, and the fuller they get, the slower they can perform.
While this won’t bother most iPhone 18 Pro owners, it does matter for anyone who fills the drive with loads of 4K video or huge file transfers — the exact people who might opt for Apple’s highest-capacity devices.
Amidst an ongoing RAM and storage crunch caused by AI companies’ demands, Apple reportedly uses quad-level cell (QLC) flash storage in at least some of its 1TB, and possibly 2TB, iPhone 18 Pros. Models with less storage (256GB and 512GB) reportedly use better triple-level cell (TLC) storage. QLC packs four bits into each memory cell instead of three, which boosts capacity but translates to more work for the chip because a single changed bit forces all four to be rewritten. QLC is also less durable than TLC.
Bilibili channel Homolab put a 1TB iPhone 18 Pro Max through real-world storage benchmarks, comparing it against the 512GB model. These models use different flash memory types, and that choice seems to have shaped everything that follows.
In standard 4K read tests, the gap was pretty small, but the 512GB model edged out the 1TB version by somewhere around 11%. Under a tough, mixed read-write test at low queue depths, the 512GB model pulled ahead by 38%. That gap lessened to just 12% under higher queue depths, where more tasks run at once.
To downplay that weakness, Apple builds in layers of buffering into all iPhone 18 Pro models. A small single-level cell (SLC) cache absorbs quick bursts at speeds above 3,000 megabytes per second. Once that fills up, a second buffer kicks in. That only runs at 578 megabytes per second. After both buffers fill up, the data hits the raw QLC storage.
This is where things get ugly. Under sustained write tests, the 1TB drive’s raw storage averaged just 79.4 megabytes per second. At its worst, it dropped down to just 25.6 megabytes per second.
A fuller drive makes the slowdown even worse
Free space matters more than you’d think. With the iPhone 18 Pro Max’s drive at just 60% capacity, the fast SLC cache shrank from 250GB to just 58GB. The secondary buffer slowed down as well, averaging just 396 megabytes per second instead of 578 megabytes.
And once both buffers ran out under that scenario, raw QLC write speeds averaged just 45 megabytes per second. Occasionally, the drive even dipped to just 1.1 megabytes per second, a rate slower than many budget microSD cards.
The results support an earlier rumor that suggested Apple’s higher-capacity iPhone 18 Pro models would trade storage speed for extra capacity.
Most iPhone 18 Pro Max owners won’t notice, but still
Keep in mind that this is a worst-case scenario. Any phone’s storage would struggle under a synthetic workload designed to exhaust every buffer. Regular tasks like texting, browsing and casual photography are well within the cache’s comfort zone. And even most gaming sessions don’t come close to triggering the slowdown.
The speed dip only shows up after tens of gigabytes are written in a continuous stretch. Think extended 4K or ProRes video recording, massive file transfers, and full backup restores. However, those also happen to be the exact tasks that push some buyers toward the 1TB or 2TB models in the first place. It makes the storage type an odd fit for the people most likely to pay extra for it.
Apple leaker Ice Universe praised Apple’s clever workarounds while calling out the inherently contradictory nature of putting less-capable NAND storage in its most expensive models.
“Apple’s storage controller and caching strategy are genuinely impressive,” Ice Universe wrote Monday on X. “In most everyday scenarios, they can hide many of QLC’s weaknesses extremely well. But cache can only hide those weaknesses. It cannot change the underlying physical characteristics of QLC NAND. If another flagship brand did this on its most expensive high-capacity models, I can only imagine how brutal the reaction would be.”
Anurag Chawake is a tech-focused writer specializing in smartphones, apps and consumer technology. His interest in computers began during the Windows 98 era, eventually leading him to explore everything from operating systems to mobile devices and PC hardware. Anurag previously contributed to The Indian Express, covering Apple, Android, gaming and the broader technology landscape.
