iPhone 18 Pro Max storage test raises concerns for the Pro workflows Apple markets it for

A 1TB iPhone 18 Pro Max equipped with QLC NAND briefly saw its write throughput collapse to 1.1 MB/s after its caches were exhausted in a storage benchmark. The handset also trailed a TLC-equipped 512GB iPhone 18 Pro in HOMOLAB's random and mixed storage tests.

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Storage-testing channel HOMOLAB used FIO to compare the two devices. During 128K sequential writes beginning with the nearly empty 1TB handset, its dynamic SLC cache delivered more than 3,000 MB/s and covered approximately 250GB. Performance then fell to an average of 578 MB/s in a pseudo-TLC stage before the QLC write-back phase averaged 79.4 MB/s, with a minimum of 25.6 MB/s.

HOMOLAB repeated the benchmark after filling 60% of the phone's storage. Its SLC cache then shrank to 58GB, pseudo-TLC performance averaged 396 MB/s, and the QLC write-back stage averaged 45 MB/s while briefly reaching the widely cited 1.1 MB/s minimum.

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That minimum should not be mistaken for the phone's normal write speed or its performance whenever the storage is 60% full. It appeared late in a synthetic worst-case workload after prolonged continuous writing, and the published graph does not reveal how long it persisted.

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Frequently Asked Questions

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Question #1

How does the iPhone 18 Pro Max's 1TB QLC storage behave during long 4K or ProRes recording sessions?

During prolonged sustained writes, the 1TB QLC storage can start fast but then fall sharply once its faster caches are exhausted. In HOMOLAB's test, the nearly empty phone began above 3,000 MB/s, then dropped to 578 MB/s before the QLC write-back stage averaged 79.4 MB/s, and with the phone 60% full that final stage averaged 45 MB/s and briefly hit 1.1 MB/s. That means long high-bitrate 4K or ProRes recording could run into much slower storage behavior after extended continuous writing.

Question #2

What happens to the iPhone 18 Pro Max's storage performance when the phone is already partially full?

When the 1TB iPhone 18 Pro Max was filled to 60% of its storage, its dynamic SLC cache shrank from about 250GB to 58GB. In the benchmark, pseudo-TLC performance fell to 396 MB/s and the QLC write-back stage averaged 45 MB/s, with a brief minimum of 1.1 MB/s. The article says that lowest figure came during a prolonged synthetic worst-case write test, not as the phone's normal speed at 60% full.

Question #3

Why did the 1TB iPhone 18 Pro Max trail the 512GB iPhone 18 Pro in random and mixed storage tests?

It appears to have trailed because the 1TB model used QLC NAND, while the 512GB iPhone 18 Pro used TLC. HOMOLAB's testing showed the 1TB phone's performance falling after its faster caches were exhausted, which is where random and mixed workloads would be more likely to expose the slower underlying storage.

Question #4

Could large file transfers or backup restores hit the slowest write stage on the iPhone 18 Pro Max?

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The finding should not be completely disregarded, however. Everyday activities such as messaging, browsing, and casual photography are unlikely to exhaust the faster caches, but extended high-bitrate 4K or ProRes recording, very large file transfers, and backup restoration could expose the slower stage. Those workloads are particularly relevant because Apple explicitly markets its Pro models towards creators and professional users.

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