My understanding is that a lot of AI data centers are still heavily relying on spinning HDDs, which is why seagate, western digital are selling more HDDs than ever before.
https://s24.q4cdn.com/101481333/files/doc_financials/2026/q3...
"Hard Drive exabyte shipments of 199EB, up 39% YoY, with ~90% shipped to data center customers"
"Data center revenue of $2.5B, up 55% YoY, driven by strengthening cloud and enterprise demand"
And an article: https://www.seagate.com/stories/articles/the-ai-era-doesnt-r...
I know that a lot of cloud storage has tiered models, where the "expensive, but faster" tiers are SSDs, but then the slower cheaper tiers are HDDs, and the "cold storage" can be HDDs that are turned off all the way to tiers like AWS's S3 "deep archive glacier" tier being tape drives.