Fine-Grained Device Management in an Interactive Media Server Raju Rangaswami, Zoran Dimitrijevic, Edward Chang, and Shueng-Han Gary Chan IEEE Trans. on Multimedia, Dec 2003

Outline Introduction Interactive media proxy Device profiling Device management High-level data organization Low-level data organization IO scheduling System evaluation

Introduction Interactive media Fast-forward Interactive media proxy (IMP) Transform non-interactive broadcast or multicast streams into interactive ones for servicing a large number of end users.

Interactive Media Proxy (IMP) Device profiling Collect detailed disk parameters to manage a device more effectively. Device management Perform fine-grained device management to improve the overall disk access efficiency.

Disk profiling The authors present a SCSI disk profiling tool that extracts detailed disk parameter. Why disk profiling is necessary? Inaccurate information (worst case assumption) Dynamic information (ex: file fragmentation) Manufacturing variance

Device management High-level data organization Low-level disk placement IO scheduling

High-level data organization For fast-scan Skip B frames Display a P frame only if the corresponding I frame is also included. Adaptive tree scheme Use a truncated binary tree to store videos. Each level of the tree forms a substream and is stored as a sequential file.

Truncated binary tree original I + P sampled I

Adaptive tree scheme Height (h) The number of levels The number of supported fast-scan streams Density (η) Range from 0 to 1 The smaller η eliminates some tree level and decreases the tree density.

Low-level disk placement (1/2) Zoning placement Zone – multiple cylinders Combine similar bit-rate streams in the same logical zone. Outer zones have higher data-transfer rate. High bit-rate streams should be stored in fast zones. (to maximize throughput) Cylinder placement Exploit the deterministic nature of write streams and use a best-effort approach for reads.

Low-level disk placement (2/2) When any write stream uses up its allocated cylinders, a new set of free cylinders within the same zone and adjacent to the previous cylinder set is allocated. Cylinder placement maintains the same relative cylinder distance between the stream pairs. Minimize IO variability. The seek overhead for switching from one write stream to the next write stream requires the disk to seek typically less than 50 cylinders. (almost equal to the minimum seek time for a single cylinder) S1S1 S2S2 S3S3 S1S1 S2S2 write …

IO scheduling Goals Maximize throughput Minimize response time Step-sweep IO scheduling Using Cylinder Placement, the seek overheads for write streams can be minimized. Thus, step-sweep schedules write streams optimally.

Step-sweep IO scheduling

System evaluation Truncated Binary Tree (TBT) η = 1 Partial TBT (PTBT) η = 0.5 Sequential (SEQ) η = 1/h (original video stream) Reduce seek overhead for writes. Suffer from fast-scan.

SEQ v.s. PTBT v.s. TBT SEQ reduces seek operations

Zoning Placement Zoning placement improves throughput for read-intensive loads.

Cylinder Placement

Step-Sweep

Cumulative Effect