Increasing scale and the need for rapid response to changing requirements are hard to meet with current monolithic cluster scheduler architectures. This restricts the rate at which new features can be deployed, decreases efficiency and utilization, and will eventually limit cluster growth. We present a novel approach to address these needs using parallelism, shared state, and lock-free optimistic concurrency control.

File system virtual appliances (FSVAs) address the portability headaches that plague file system (FS) developers. By packaging their FS implementation in a virtual machine (VM), separate from the VM that runs user applications, they can avoid the need to port the file system to each operating system (OS) and OS version. A small FS-agnostic proxy, maintained by the core OS developers, connects the FSVA to whatever OS the user chooses. This article describes an FSVA design that maintains FS semantics for unmodified FS implementations and provides desired OS and virtualization features, such as a unified buffer cache and VM migration. Evaluation of prototype FSVA implementations in Linux and NetBSD, using Xen as the virtual machine manager (VMM), demonstrates that the FSVA architecture is efficient, FS-agnostic, and able to insulate file system implementations from OS differences that would otherwise require explicit porting.

A fault-scalable service can be configured to tolerate increasing numbers of faults without significant decreases in performance. The Query/Update (Q/U) protocol is a new tool that enables construction of fault-scalable Byzantine fault-tolerant services. The optimistic quorum-based nature of the Q/U protocol allows it to provide better throughput and fault-scalability than replicated state machines using agreement-based protocols. A prototype service built using the Q/U protocol outperforms the same service built using a popular replicated state machine implementation at all system sizes in experiments that permit an optimistic execution. Moreover, the performance of the Q/U protocol decreases by only 36% as the number of Byzantine faults tolerated increases from one to five, whereas the performance of the replicated state machine decreases by 83%.

Verification of write operations is a crucial component of Byzantine fault-tolerant consistency protocols for storage. Lazy verification shifts this work out of the critical path of client operations. This shift enables the system to amortize verification effort over multiple operations, to perform verification during otherwise idle time, and to have only a subset of storage-nodes perform verification. This paper introduces lazy verification and describes implementation techniques for exploiting its potential. Measurements of lazy verification in a Byzantine fault-tolerant distributed storage system show that the cost of verification can be hidden from both the client read and write operation in workloads with idle periods. Furthermore, in workloads without idle periods, lazy verification amortizes the cost of verification over many versions and so provides a factor of four higher write bandwidth when compared to performing verification during each write operation.