FaaS in the age of (sub-)μs I/O: a performance analysis of snapshotting

Although serverless computing brings major benefits to developers, the widespread adoption of Function-as-a-Service (FaaS) creates severe challenges for the cloud providers. Irregularity in function invocation patterns and the high cost of cold starts has led them to allocate precious DRAM resources to keep function instances always warm , a clearly sub-optimal and inflexible approach. To cope with this issue, both state-of-the-art and state-of-practice approaches consider snapshotting as a viable mitigation, thus directly associating cold start latency with storage performance. Prior studies consider storage to be inert, rather than the evolving hierarchy that it truly is. In this work, we evaluate cold start and warm function invocations on instances restored from snapshots residing on devices across different layers of the modern storage hierarchy. We thoroughly analyze and characterize the observed behavior of multiple workloads and identify fundamental trade-offs among the devices. We conclude by motivating and providing suggestions for the inclusion of the modern storage hierarchy as a decisive factor in serverless resource provisioning.