Everyone Loves File

Abstract

Oracle File Storage Service (FSS) is an elastic filesystem provided as a managed NFS service. A pipelined Paxos implementation underpins a scalable block store that provides linearizable multipage limited-size transactions. Above the block store, a scalable B-tree holds filesystem metadata and provides linearizable multikey limited-size transactions. Self-validating B-tree nodes and housekeeping operations performed as separate transactions allow each key in a B-tree transaction to require only one page in the underlying block transaction. The filesystem provides snapshots by using versioned key-value pairs. The system is programmed using a nonblocking lock-free programming style. Presentation servers maintain no persistent local state making them scalable and easy to failover. A non-scalable Paxos-replicated hash table holds configuration information required to bootstrap the system. An additional B-tree provides conversational multi-key minitransactions for control-plane information. The system throughput can be predicted by comparing an estimate of the network bandwidth needed for replication to the network bandwidth provided by the hardware. Latency on an unloaded system is about 4 times higher than a Linux NFS server backed by NVMe, reflecting the cost of replication. FSS has been in production since January 2018 and holds tens of thousands of customer file systems comprising many petabytes of data.