Object storage service

Design an S3-like object-storage service. Constraints: 11 nines (99.999999999%) of durability, exabyte-scale total capacity, objects from 1 KB to 5 TB, read-heavy at roughly 20:1 read/write, p99 GET latency under 100 ms for warm objects, and strong read-after-write consistency for new PUTs. Walk the request path, the metadata layer, and how you place and protect bytes at this scale.