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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

MMFS PERFORMANCE EVALUATION Impact of prefetching optimization Parameters of experiment

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

MMFS PERFORMANCE EVALUATION Impact of prefetching optimization Reverse playback

MMFS PERFORMANCE EVALUATION Impact of prefetching optimization Fast forward playback

MMFS PERFORMANCE EVALUATION Impact of prefetching optimization Fast reverse playback

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

MMFS PERFORMANCE EVALUATION Impact of prioritized RT disk scheduling Effect of RT load

MMFS PERFORMANCE EVALUATION Impact of synchronization support Multi-Strand Playback

MMFS PERFORMANCE EVALUATION Impact of synchronization support

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

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

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

REFERENCES Niranjan, T. N. File System Support for multimedia applications. PhD thesis, SUNY at Stony Brook, December At 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

Q & A Thank You !