Problem · seen at 1 company
Placement precedes the access pattern
You have to decide where the data lives before you know how it'll be read — and that bet is expensive to unwind.
The wall
A placement decision (device, tier, region, replication level) must be made before the access pattern that would justify it exists — only files/objects whose placement decision precedes its evidence belong to this class. Systems where prediction merely optimizes an answer to some other wall (an ML-tuned cache atop a solved placement, a forecast feeding an autoscaler) do NOT belong: there prediction is the answer, not the wall.
Same wall, 1 system
Google
Google Cloud Blog
Where a file should live depends on a future visible only after placement. Read the breakdown →