iPhone 18 Pro Max 1TB storage drops to 1.1MB/s under extreme loads

Testing by Bilibili channel Homolab found that the 1TB iPhone 18 Pro Max uses QLC flash instead of TLC, causing severe slowdowns under sustained writes. Once SLC and TLC buffers are exhausted, speeds fall to 79.4MB/s and occasionally 1.1MB/s. Normal usage is unaffected.

• Q1T1 benchmark: 512GB scored 11,285 vs 8,168 for 1TB — a 38% gap
• At 60% capacity, SLC cache shrinks from about 250GB to 58GB
• QLC write speeds average 45MB/s, occasionally hitting 1.1MB/s
• SLC cache runs near 3000MB/s, TLC buffer at 578MB/s