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Implementation and Evaluation of a Multimedia File System

This paper presents MMFS, a file system that extends UFS to support multimedia applications. It offers functionalities for synchronized retrieval, editing support, caching and prefetching optimizations, and real-time disk scheduling. The performance evaluation compares MMFS with UFS and measures the impact of prefetching optimization on response time and playback performance.

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Implementation and Evaluation of a Multimedia File System

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  1. Implementation and Evaluation of a Multimedia File System • T.N.Niranjan • Tzi-cker Chiueh • Gerhard A. Schloss • Department of Computer Science • State University of New York at Stony Brook • 1997 IEEE • Presented by Sharon Shen

  2. OVERVIEW • Introduction • Related Work • MMFS Design • Performance Evaluation • Conclusions and future work

  3. INTRODUCTION • Multimedia unique demands in file system • MMFS extends UFS • Supports a two dimensional file structure • Single medium editing • Multiple-media playback environments • A fully functional file system based on the VFS

  4. INTRODUCTION • Classification of multimedia applications • Playback oriented • Concerned with real-time constraints and synchronized retrieval • Development oriented • Require system support to manipulate compositions

  5. INTRODUCTION • MMFS offers a set of functionalities for multimedia support • Synchronized multi-stream retrieval • Editing support • Caching and prefetching optimizations • Real-time disk scheduling

  6. RELATED WORK • UCSD multimedia server • CMFS • Mitra & SBVS • IBM Tiger Shark • YARTOS

  7. RELATED WORK • Tactus toolkit & Acme I/O Server • Audition audio system • MMFS could not provide real-time guarantees to multimedia playback • Vagaries of the FreeBSD process scheduler • Lack of admission control • Re-implementation on Unix OS augmented with real-time support make this feature feasible

  8. MMFS DESIGN • Extends the UNIX file structure • A single-medium strand abstraction • An MM file construct: tie multiple strands • An MM file is associated with unique mnode • Mnode contains the metadata of the MM file • Mutimedia-specific metadata of each strand (recording rate,logical block size, the size of the application data unit)

  9. MMFS DESIGN • Reduction of the “impedance mismatch” between the multimedia applications and the file system • Used for low-level optimization • MMFS API • Add an extra argument mminfo • Add/Remove strands from an MM file • Insert/Delete data from strands

  10. MMFS DESIGN Prefetching • Unix file system • Sequential reads are common • Each open file is associated with a read-ahead length(v_ralen) in its vnode • Not sequential readprefetching is avoid and exponential back-off of v_ralen is initiated

  11. MMFS DESIGN Prefetching • Playback of a video in reverse • UFS identify non-sequential readreduce the degree of prefetching • MMFS allows the application to advise the file system reverse the direction • Setting mminfo->direction to REVERSE • Passing mminfo as an argument to mmread

  12. MMFS DESIGN Prefetching • Playback of a video in fast-forward • UFS Prefetching ( issue read-aheads for unnecessary blocks)

  13. MMFS DESIGN Prefetching • Playback of a video in fast-forward • MMFS perform intelligent prefetching • Applications communicate MMFS • Setting the fields in mminfo (retrieval rate,direction,whether frames skip) • Degree of prefetching is maintained at a high level Note: It does not work for compressed data streams

  14. MMFS DESIGN Prioritized real-time disk scheduling • UFS using SCAN • Order the request by the position of the requested physical block on the disk surface • nonRT operations queued with RT multimedia operations

  15. MMFS DESIGN Prioritized real-time disk scheduling • MMFS using priority • Higher priority = RT request, lower priority = nonRT request • Non-preemptive Scheduling • Assign a deadline with each mmread request • Use Earliest Deadline First scheduling for RT use SCAN for nonRT request • Starvation possible for nonRT

  16. MMFS DESIGN Support for synchronization • Quality of synchronization measured by the amount of skew • MMFS considers each strand as a temporally continuous stream of data • Specify mmbind, synchronized retrieval the given strands • MMFS constructs a round-robin retrieval schedule for these strands • An mmunbind call issued when synchronization is no longer required

  17. MMFS DESIGN Support for Editing • UFS use write, truncate system calls for small size file • Multimedia editing large uncompressed files • MMFS provide mminsert and mmdelete

  18. MMFS PERFORMANCE EVALUATION Evaluation Environment • Multimedia data residing in local IDE disk of Pentium-90 • Compare MMFS with UFS of FreeBSD 2.0.5

  19. MMFS PERFORMANCE EVALUATION Impact of prefetching optimization • Parameters of experiment

  20. MMFS PERFORMANCE EVALUATION Impact of prefetching optimization • Response Time: time taken between the issuance of read request and the reception of the request data • Delayed: If the response time is more than 130% of the frame duration • Performance metric: fraction of delayed frames

  21. MMFS PERFORMANCE EVALUATION Impact of prefetching optimization • Reverse playback

  22. MMFS PERFORMANCE EVALUATION Impact of prefetching optimization • Fast forward playback

  23. MMFS PERFORMANCE EVALUATION Impact of prefetching optimization • Fast reverse playback

  24. MMFS PERFORMANCE EVALUATION Impact of prioritized RT disk scheduling • Effect of nonRT load

  25. MMFS PERFORMANCE EVALUATION Impact of prioritized RT disk scheduling • Effect of RT load

  26. MMFS PERFORMANCE EVALUATION Impact of synchronization support • Multi-Strand Playback

  27. MMFS PERFORMANCE EVALUATION Impact of synchronization support

  28. CONCLUSIONS & FUTURE WORK • UFS assumptions and design decision are not appropriate for multimedia • MMFS prefetching optimization allow applications to playback streams at higher access rate and different directions • MMFS disk scheduler maintains the performance of the multimedia application when RT and nonRT application are simultaneously active

  29. CONCLUSIONS & FUTURE WORK • MMFS editing primitives offer an excellent response to development applications • MMFS bridges the gap between generic file systems and special-purpose servers • MMFS provides real-time process scheduling to meet QoS requirements

  30. CONCLUSIONS & FUTURE WORK • The idea embedded in MMFS are widely applicable to any general-purpose file system • Many enhancements to the current implementation are possible • The impact of variable-rate compression on MMFS optimizations have to be studied • The feasibility of extending MMFS to a distributed environment deserves investigation

  31. REFERENCES • Niranjan, T. N. File System Support for multimedia applications. PhD thesis, SUNY at Stony Brook, December 1996. At http://www.cs.sunysb.edu/~niranjan/thesis.ps.gz • Niranjan, T. N. and Schloss. F. State-based buffer-cache design for a multimedia file system. In Proc. Of the Sixth Int. Workshop in Network and Operating System Support for Digital Audio and Video(NOSSDAV), April 1996

  32. Q & A Thank You !

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