Fine-Grained Device Management in an Interactive Media Server

Raju Rangaswami, Zoran Dimitrijevic, Edward Chang, and Shueng-Han Gary ChanIEEE 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 correspondi

ng 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 i

s stored as a sequential file.

Truncated binary tree

original

I + P

sampled I

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 de

creases 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)

S1S2S3S1S2

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