GoKawiil1TB iPhone 18 Pro Max's QLC storage crawls 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 flash for higher storage capacity, suffers major write speed drops once its cache buffers are exhausted. Sustained writes can fall to as low as 25.6 MB/s fresh out of the box, and to just 1.1 MB/s once the phone is 60% full, far behind the 512GB TLC-based iPhone 18 Pro.
Apple's shift to QLC memory for larger storage tiers packs more data into the same chip space but sacrifices real-world speed once cache runs out, meaning heavy users transferring large files or filling up their storage could notice sluggish performance. This trade-off highlights how storage capacity marketing can mask meaningful performance differences between iPhone variants that cost the same tier price.
- QLC NAND in the 1TB iPhone 18 Pro Max trades speed for higher capacity versus TLC-based models.
- Sustained write speeds can crash to as low as 25.6 MB/s when cache is exhausted, and 1.1 MB/s at 60% capacity.
- The TLC-based 512GB iPhone 18 Pro consistently outperforms the QLC model in mixed and sustained workloads.
SanDisk Extreme Portable SSD 1TB — If your iPhone 18 Pro Max's QLC storage bogs down during heavy file transfers or 4K video dumps, offloading to a fast external SSD keeps your workflow smooth. The SanDisk Extreme Portable SSD offers reliable, consistent write speeds for backing up photos and videos without waiting on your phone's internal storage bottlenecks. It's a handy companion for content creators who shoot a lot of high-resolution footage on their iPhones.
See SanDisk Extreme Portable SSD 1TB 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”
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