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Boxwood: Distributed Data Structures as Storage Infrastructure Lidong Zhou Microsoft Research Silicon Valley Team Members: Chandu Thekkath, Marc Najork,

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Presentation on theme: "Boxwood: Distributed Data Structures as Storage Infrastructure Lidong Zhou Microsoft Research Silicon Valley Team Members: Chandu Thekkath, Marc Najork,"— Presentation transcript:

1 Boxwood: Distributed Data Structures as Storage Infrastructure Lidong Zhou Microsoft Research Silicon Valley Team Members: Chandu Thekkath, Marc Najork, Nick Murphy

2 10/27/2003 Boxwood 2 Trends in Storage Systems: Distribution, Virtualization, and Abstractions The case for distributed storage architecture Enables incremental expandability Benefits performance and reliability Virtualization facilitates management Scalability, automatic reconfiguration, load balancing, and fault tolerance Abstractions for managing complexity

3 10/27/2003 Boxwood 3 Going Beyond Virtual Disks Virtual disk provides a low-level abstraction Complexity pushed to each client and duplicated Limited intelligence due to lack of structural info. Advantages of higher-level abstractions Reduce client complexity and eliminate duplication Exploit structural information for better load balancing, pre-fetching, and caching There is no universal abstraction

4 10/27/2003 Boxwood 4 Boxwood System Architecture Supports multiple data abstractions Space abstraction: Segments named by UIDs Structure abstractions (B-Link Tree, Hash Table, Skip List) UID Space Structure Abstractions B-Link TreeHash Table

5 10/27/2003 Boxwood 5 UID Space Abstraction Segments in a flat UID space UID names segments Deallocated UIDs are never reused Offloads address management from clients Clients can provide hints (e.g., for co-location) A virtualization layer Distributed, fault tolerant, and incrementally expandable Performs simple capacity and load balancing

6 10/27/2003 Boxwood 6 UID Space: Design and Implementation Client Space Clerk Consensus (Paxos) UID Space Disks Hash Table B-Link Tree

7 10/27/2003 Boxwood 7 Higher-Level Structure Abstractions UID Space emphasizes universality and simplicity Structure abstractions more attractive for sophisticated clients Co-location, pre-fetching, and caching strategies supported inside Boxwood Better abstractions for databases and file systems First Boxwood structure abstraction: B-Link trees Supports tree creation/destruction, insert, delete, lookup, and enumeration A good abstraction with wide applicability Enough complexity to expose fundamental issues

8 10/27/2003 Boxwood 8 B-Link Tree Layer Built on the UID space Highly concurrent B- Link tree operations with distributed locking Logging/recovery to ensure atomicity of B- Link tree operations Distributed Locking UID Space B-Link Tree B-Link Tree

9 10/27/2003 Boxwood 9 Current Status UID space and B-Link tree modules Distributed UID space with capacity balancing B-Link tree algorithm with distributed locking Logging/recovery for tolerating transient failures Paxos consensus On-going Work Run-time verification of the B-Link tree algorithm (Shaz Qadeer and Serdar Tasiran) A distributed file system on Boxwood abstractions

10 10/27/2003 Boxwood 10 File System on Boxwood: A High-Level Design B-Link tree abstraction is ideal for directories and meta-data Files are implemented using both B-Link tree abstraction and UID space abstraction B-Link trees for i-node: mapping from file offsets to (UID, offset) UID space for actual user data store

11 10/27/2003 Boxwood 11 File System on Boxwood: The Architecture Distributed Locking UID Space B-Link Tree File Server File Server B-Link Tree Client NFS/CIFS

12 10/27/2003 Boxwood 12 Future Work Finish module implementation load balancing automatic reconfiguration chained de-clustered disk More abstractions and clients to explore utility, generality, and flexibility of Boxwood

13 10/27/2003 Boxwood 13 Related Work Distributed Storage/Operating Systems Virtual/Logical disks File systems Database systems Scalable Distributed Data Structures Linear Hash Table (LH) and its variants (Litwin, present) Scalable distributed hash table (Gribble, et al., 2000) Highly concurrent B-tree (Lehman&Yao, 1981; Sagiv, 1986)

14 10/27/2003 Boxwood 14 Early Experience and Observations Virtualized distributed storage infrastructure that exports good abstractions is promising Multiple layers of abstractions are beneficial Manages complexity Caters to the needs of a wide variety of clients Distributed file system on Boxwood is straightforward Use of a matching high-level abstraction is ideal A low-level abstraction offers more flexibility, but requires more bookkeeping A good exercise to uncover fundamental principles in scalable/reliable distributed systems


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