GoKawiil1TB iPhone 18 Pro Max's QLC storage slows to 1.1 MB/s under heavy write loads
Testing by Bilibili channel Homolab found that the 1TB iPhone 18 Pro Max, which uses QLC NAND, suffers major performance drops compared to the 512GB TLC-based iPhone 18 Pro. Once its SLC and secondary TLC caches are exhausted, sustained writes fall to about 79.4 MB/s and can dip as low as 25.6 MB/s, worsening to just 1.1 MB/s once the drive is 60% full.
GoKawiil's interpretation of the reporting above, not reported fact.
QLC NAND lets Apple offer larger storage tiers cheaply, but the tradeoff is real-world slowdowns during heavy file transfers, video recording, or app installs, especially as the device fills up over time. This highlights a growing tension between storage capacity marketing and sustained performance, something buyers of high-capacity iPhones may not notice until months of use erode available cache space.
- QLC NAND in the 1TB iPhone 18 Pro Max trails TLC storage in the 512GB Pro by up to 38% in mixed workloads.
- Sustained writes can crash to as low as 1.1 MB/s once cache is exhausted and storage is 60% full.
- Higher storage capacity via QLC comes at a real performance cost, especially for heavy or prolonged data writes.
SanDisk Extreme Portable SSD — If your iPhone 18 Pro Max's QLC storage is choking on heavy write workloads, offloading large files like 4K videos to a fast external SSD is a smart workaround. The SanDisk Extreme Portable SSD offers quick transfer speeds and rugged durability, making it a great companion for creators dealing with storage bottlenecks.
See SanDisk Extreme Portable SSD on Amazon → Affiliate link — we may earn a commission on purchases, at no extra cost to you. Product picked by AI based on this article; it is not a tested recommendation.Source: tomshardware.com — Kunal Khullar, 2026-09-21
Published there as: “iPhone 18 Pro Max storage can drop lower than a hard drive at 1.1 MB/s during heavy writes — QLC NAND offers higher capacity but reportedly suffers 38% drop compared to TLC-based Pro”
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