Buying 1TB of iPhone 18 Pro storage may not guarantee the same sustained write performance from one phone to another. A new teardown and stress test found QLC NAND in one 1TB iPhone 18 Pro Max, while a 512GB iPhone 18 Pro used TLC NAND, exposing a potential problem for creators who record very large files.
In HOMOLAB’s original test, the 1TB Pro Max was filled to roughly 60 percent before sustained writes exhausted its faster caches. During the direct-to-QLC stage, the phone averaged about 45MB/s and briefly fell as low as 1.1MB/s. That is an extreme cache-exhaustion result, not the phone’s normal write speed.
Why the result matters for video
Apple markets the Pro models heavily to filmmakers. Its technical specifications list ProRes video up to 4K at 120 fps with external recording, alongside ProRes RAW and Apple Log 2. Those demanding formats can create long, sustained storage workloads, which is where a cache-exhausted drive matters more than it does while saving photos or downloading apps.
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However, the test does not show that every 1TB iPhone 18 Pro or Pro Max contains QLC NAND. Supply appears to be mixed between QLC and TLC, and Apple does not disclose the NAND type in its specifications or at checkout. HOMOLAB also did not directly test a 2TB model, so the result cannot be extended to that tier.
Creators should buy for their workflow
The finding makes Apple’s already expensive storage upgrade ladder harder to judge. More capacity still provides more room, but buyers cannot currently check whether a particular phone uses TLC or QLC before purchase.
A 512GB model may be the more conservative choice for someone worried about this specific result, though one tested unit does not guarantee that every 512GB phone uses TLC. For sustained professional recording, a fast compatible external SSD is the clearer safeguard. Apple itself requires external recording for the highest 4K120 ProRes mode, and our Pro and Pro Max video comparison explains that both sizes share the same capture specification.
Creators who mainly shoot shorter clips may never reach the direct-QLC stage seen in this stress test. Anyone deciding between capacities should weigh the result alongside actual shooting duration, file offload habits, and the fact that Apple does not publish usable capacity for any tier.
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