HydraFS: a High-Throughput File System for the HYDRAstorContent-Addressable Storage System

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Authors•Cristian Ungureanu

•Benjamin Atkin•Akshat Aranya•Salil Gokhale

•Stephen Rago•Grzegorz Calkowski

•Cezary Dubnicki•Aniruddha Bohar

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Contents• HYDRAstor Introduction• Content-Addressable Storage (CAS)• Problems and Solutions for CAS• Challenges for the new implementation• Filesystem layout and software architecture• Read/write processing, metadata cleaning, deletion

• Conclusion

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HYDRAstor Introduction•Multi-node CAS system•Stores blocks at configurable redundancy levels

•Supports high-throughput R/W for large blocks•Use for:

•Backup solutions•DR solutions•Data archive

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NEC HYDRAstor•HYDRAstor architecture introduced in March 2007

•Conducts R&D in the USA, Japan, Germany, China

•High performance, capacity-optimized, and highly available storage solutions, for Enterprise backup, long-term data archive, and DR solutions

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Competitors•EMC Corporation

• Centera, DataDomain

•Hewlett-Packard• Information Access Platform (RISS)

•Hitachi Data Systems• Content Archive Platform (HCAP)

•IBM• DR550

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Content-Addressable Storage•A Content-Addressable Storage (CAS): •Elimination of duplicate blocks •Gives high throughput for streaming access

•Once saved an object, can’t be deleted until retention expired

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Problems with CAS System•Absence of standardized API,•makes barrier to use of CAS with existing applications

•Have to rewrite applications to use with the CAS-specific API

•Applications have to deal with unique characteristics of CAS. • Immutability of blocks•High latency on operations

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Solution•Built HydraFS filesystem on top of CAS system making an interface

•Support distributed CAS systems

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CAS System

HydraFS

App 1 App 2 App 3

Solution cont…•HydraFS presents standard interface to effective use of CAS system without requiring changes in applications

•Gain storage performance by mapping best access patterns of the applications

•HydraFS increases R/W performance of HYDRAstor by 82–100%

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Challenges•Immutable block size•High latency•Chunking algorithm to determine block boundaries

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Filesystem Design Achievements•High throughput for sequential R/W

•Minimized dependent I/O•Guarantees data availability•Supports both local & remote FS access

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Filesystem Layout

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•Designed as a DAG•Root stores searchable block which holds super block

•Superblock holds imap and current FS version

Software Architecture

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•Implemented as user-level processes

•Fileserver manages FS interface

•Commit server generates new FS version

Write Processing•Fileserver buffers file write data•Apply content-defined chunking algorithm

•Create new variable size blocks, marked ‘dirty’

•Write dirty block to disks•Uncommitted block table – modified FS metadata

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Metadata Cleaning•Commit server creates FS new super block,

•After that, fileserver can clean its dirty metadata

•Generates new version of the FS

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Admission Control•Mechanism to control memory usage•Define memory for objects, Ex: data blocks, inode

•New events are allowed when memory available, otherwise event blocks

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Read Processing•Get read-ahead metadata into in-memory

•Content addresses of this range retrieve from inode’s B-tree

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Deletion•Remove the pointer to the data block from namespace. Storage space is left

•After new FS created, old version marked for deletion

•Number of retain FS ver. are configurable

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Conclution•HydraFS outcome:•High throughput RW access•High duplicate elimination rate

•Evaluation results:•Efficient and support up to 82% for read and 100% for writes

•Best suitable for:•Backup applications and repositories

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Thank you…

Questions?

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