HDD vs NAND Flash: Why AI Data Centres Need Both
AI data centres need both hard disk drives and NAND flash because they solve different problems. Flash supplies the low latency and high IOPS required to feed accelerators with model weights, key value caches and vector indexes. HDDs supply the cheapest, most sustainable capacity per terabyte for the massive training corpora and long lived outputs that keep growing as models run. Vendors describe this as a tiered design where flash deepens the stack rather than replacing capacity disks.
On cost and sustainability, HDDs still anchor the capacity tier. Seagate reports an approximate 6ร acquisition cost per terabyte advantage for HDDs over NAND based SSDs and highlights much lower energy and embodied carbon per TB, which matters at hyperscale. On performance and endurance mechanics, flash stores charge in semiconductor cells and delivers very low latency with high random IOPS, but it wears with use and therefore needs controllers, ECC, wear leveling and over provisioning to manage lifetime, as explained by Micron.
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