• Generalized Caching as a Service

 Caching has been a consistent tool of designers of high-performance, scalable computing systems, 
 but it has been deployed in so many ways that it can be difficiult to standardize and scale in 
 cloud systems. This project elevates the use of caching in cloud-scale storage system to a 
 “first-class citizen” by designing and implementing generalized Caching-as-a-Service (CaaS). 
 CaaS defines transformative technology along four complementary dimensions. First, it defines 
 a new abstraction and architecture for storage caches whereby storage stacks can easily embed 
 lightweight CaaS clients within a distributed compute infrastructure. Second, CaaS formulates 
 and theoretically analyzes distributed caching algorithms that operate within the CaaS service 
 such that individual CaaS server nodes cooperate towards achieving globally optimal caching 
 decisions. Third, the distributed CaaS clients and servers are co-designed to achieve strict 
 durability and fault-tolerance in their implementations. And finally, all of the CaaS 
 advancements are driven by insights generated from a detailed whole-system simulator that 
 models the diverse cache devices, network configurations, and application demand.

• Cacheus

  Recent advances in machine learning open up new and attractive approaches 
  for solving classic problems in computing systems. For storage systems, 
  cache replacement is one such problem because of its enormous impact on 
  performance. CACHEUS represents a new class of fully adaptive, 
  machine-learned caching algorithms that utilize a combination of experts 
  designed to address a variety of workload primitive types. The experts 
  used by CACHEUS include the state-of-the-art ARC, LIRS and LFU, and two 
  new ones – SR-LRU, a scan-resistant version of LRU, and CR-LFU, a 
  churn-resistant version of LFU. CACHEUS using the newly proposed 
  lightweight experts, SR-LRU and CR-LFU, is the most consistently performing 
  caching algorithm across a range of workloads and cache sizes. Furthermore, 
  CACHEUS enables augmenting state-of-the-art algorithms (e.g., LIRS, ARC) 
  by combining it with a complementary cache replacement algorithm (e.g., 
  LFU) to to better handle a wider variety of workload primitive types.

• Region System

  Modern operating systems have been designed around the hypotheses that 
  (a) memory is both byte-addressable and volatile and (b) storage is block 
  addressable and persistent. The arrival of new Persistent Memory (PM) 
  technologies, has made these assumptions obsolete. Despite much of the recent 
  work in this space, the need for consistently sharing PM data across multiple 
  applications remains an urgent, unsolved problem. The Region System is a 
  high-performance operating system stack for PM that implements usable consistency 
  and persistence for application data. The region system provides support for 
  consistently mapping and sharing data resident in PM across user application 
  address spaces. Its high-performance design minimizes the expensive PM ordering 
  and durability operations by embracing a minimalistic approach to metadata 
  construction and management. Finally, the region system creates a novel IPI based 
  PMSYNC operation, which ensures atomic persistence of mapped pages across multiple 
  address spaces.

• NVM-enabled Host-side Caches

  The goals of this NVM Caching project are to:
    * develop selective caching algorithms that better utilize non-datapath 
      NVM caches on the host,
    * develop a model for component availability and failure domains leading 
      to a fault-tolerant write caching design for systems,
    * develop co-operative cache partitioning techniques for DRAM and NVM 
      enabled caches, and develop data reduction techniques for host-side NVM 
      caches.

• Non-blocking Writes

  In current operating systems, writes to pages that are not in core 
  memory require the process to block until the page can be fetched 
  from the backing store. This project investigates buffering the 
  write to a temporary page in core memory, so as to unblock the 
  process to continue computation, and applying the write 
  asynchronously. Research tasks include study and experimentation 
  with implementation techniques for deferring out-of-core page writes, 
  analysis of how scheduling and other aspects of the operating system 
  may need to be modified in order to realize the full benefits of 
  write deferral, and empirical studies to assess the performance 
  impact of write deferral on a variety of applications. By 
  incorporating non-blocking writes within the operating system, 
  applications can transparently benefit from a performance 
  improvement, without any modification to the application. The 
  potential performance benefits apply to a broad spectrum of computer 
  systems and applications. 

• Programming Abstractions for Persistent Memory

  Persistent memory systems promise a new era of computing where data 
  management is simplified significantly. For the very first time, 
  applications will be able to directly access devices that can respond 
  with latencies close to DRAM latencies and at the same time, store 
  data persistently without the intervention of the operating system 
  (OS). Fully realizing the potential of this new technology requires 
  that new applications are able to integrate access to these devices 
  and exploit their unique capabilities to the fullest with little 
  additional effort. Moreover, enabling existing applications to easily 
  transition to using this new technology will be critical to the 
  success of persistent memory technologies in the marketplace. The 
  goals of this proposal are directed towards optimal integration of 
  persistent memory devices within existing system software and ease 
  of use within existing application programming paradigms.

• Software Persistent Memory (SoftPM)

  Current high-end computing (HEC) applications explicitly manage   
  persistent data, including both application state and application  
  output. This practice not only increases development time and cost,   
  but also requires an application developer to be intimately aware   
  of the underlying platform-dependent storage mechanisms to achieve   
  good application I/O performance. The Software Persistent Memory   
  (SoftPM) project builds a lightweight infrastructure for streamlining   
  data management in next generation HEC applications. SoftPM eliminates   
  the duality of data management in HEC applications by allowing   
  applications to allocate persistent memory in much the same way   
  volatile memory is allocated and easily restore, browse, and interact   
  with past versions of persistent memory state. This simplifies the   
  implementation of three broad capabilities required in HEC applications   
  -- recoverability (e.g., checkpoint-restart), record-replay (e.g.,   
  -data-visualization), and execution branching (e.g., simulation   
  -model-space exploration).

• Generalized ERSS Tree Model

  Accurately characterizing the resource usage of an application at 
  various levels in the memory hierarchy has been a long-standing 
  research problem. The studies thus far have also implicitly assumed 
  that there is no contention for the resource under consideration. 
  The inevitable future of virtualization driven consolidation 
  necessitates the sharing of physical resources at all levels of the 
  memory hierarchy by multiple virtual machines. We present a unifying 
  Generalized ERSS Tree Model that characterizes the resource usage at 
  all levels of the memory hierarchy during the entire life-time of an 
  application. Our model characterizes capacity requirements, the rate 
  of use, and the impact of resource contention, at each level of 
  memory. We present a methodology to build the model and demonstrate 
  how it can be used for the accurate provisioning of the memory 
  hierarchy in a consolidated environment. 

• I/O Deduplication

  Duplication of data in storage systems is becoming increasingly 
  common. We introduce I/O Deduplication, a storage optimization 
  that utilizes content similarity for improving I/O performance by 
  eliminating I/O operations and reducing the mechanical delays 
  during I/O operations. I/O Deduplication consists of three main 
  techniques: content-based caching, dynamic replica retrieval, and 
  selective duplication.

• Energy Proportional Storage Systems

  The Environmental Protection Agency (EPA) estimates that energy 
  consumption at data centers could grow to 100 billion KWhr, 
  contributing to 2.9% of the total US electricity needs, by the 
  year 2011. This project investigates fundamentally new techniques 
  for building energy proportional storage systems that consume energy 
  in proportion to the I/O workload intensity. It takes the view that 
  a carefully constructed data replication based approach (instead of 
  data migration) combined with background data synchronization for 
  consistency provide more effective mechanisms for enabling dynamic 
  storage consolidation.

• Resource Management in Virtualized Data Center

  Performance models provide the ability to predict application 
  performance for a given set of hardware resources and are used for 
  capacity planning and resource management. Traditional performance 
  models assume the availability of dedicated hardware for the 
  application. In this paper, we build performance models for 
  applications in virtualized environments. We identify a key set of 
  virtualization architecture independent parameters that influence 
  application performance for a diverse and representative set of 
  applications. We propose an iterative model training technique based 
  on artificial neural networks which is found to be accurate across a 
  range of applications. 

• Active Block-Layer Extensions

  The Active Block Layer Extensions (ABLE) project presents a new 
  approach to realizing self-managing storage systems. It makes 
  two contributions. First, it creates an evolvable block layer 
  software infrastructure that substantially reduces the complexity 
  involved in building self-managing storage systems by raising the 
  level of abstraction for their development. Second, it develops a 
  theory of storage extensions that provides a logic framework for 
  analyzing extensions developed at the block layer. 

• Block reORGanization for Self-optimizing Storage Systems

  BORG is a self-optimizing storage system that performs automatic 
  block reorganization based on the observed I/O workload. BORG is 
  motivated by three characteristics of I/O workloads: non-uniform 
  access frequency distribution, temporal locality, and partial 
  determinism in non-sequential accesses. To achieve its objective, 
  BORG manages a small, dedicated partition on the disk drive, with 
  the goal of servicing a majority of the I/O requests from within 
  this partition with significantly reduced seek and rotational delays.

• EXternal Caching in Energy Saving Storage Systems

  Power consumption within the disk-based storage subsystem forms a 
  substantial portion of the overall energy footprint in commodity 
  systems. We present the design and implementation of EXCES, an 
  external caching system that employs prefetching, caching, and 
  buffering of disk data for reducing disk activity. EXCES addresses 
  important questions related to external caching, including the 
  estimation of future data popularity, I/O indirection, continuous 
  reconfiguration of the ECD contents, and data consistency.

• Semistructured Storage Systems: Storage, Data placement, Semistructured data, Semisequential placement, XML, DOM, SAX.