ACOS is Apple's geo-distributed, exabyte-scale object storage service. It serves billions of requests per day for iCloud, Apple Music, Apple TV, Apple Maps, and Apple's internal data and analytics platforms. It provides 11-nines of durability and 4-nines of availability.
The ACOS Storage Infrastructure team owns how data is encoded, placed, verified, repaired, and reclaimed inside a storage cluster. This includes erasure and replicated encoding schemes, data placement and rebalancing optimization, compaction, scrubbing and repair, durability modeling, performance tiering, and the supply chain that keeps available capacity in front of customer demand. In practice, this team determines what storage costs, how it survives in the face of software and hardware failures, and how fast it is served.