Continuous Media Storage and Retrieval - Scalable Continuous Media Streaming Systems - page 57

freed buffers are reused for the new round

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Transmission

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kd buffers

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Disk 0

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Disk 1

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Disk 2

kd 2 buffers

Figure 3.13 Offset schedule enables immediate reuse of empty buffers

T avg = Q / R

dk concurrent
transmissions

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Transmission

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Disk 0

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Disk 1

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Disk 2

Retrieve k blocks

Streams are divided into 3 groups

Figure 3.14 The split schedule can achieve constant per-disk buffer requirement regardless of the
number of disks in the striped disk array

The key in split schedule is that a media stream retrieves its data blocks from each disk not
in parallel as in the case of concurrent schedule and offset schedule, but in turns. For example,
if a media stream retrieves data block i from disk 0 in round j for transmission in round j + 1,

then in the next round j + 1 it retrieves data block i + 1 from disk 1 for transmission in round

2, and so on. Compared to the previous two schedulers, this split schedule reduces the
service round length from dT a v g seconds to T a v g seconds. Therefore, in addition to reusing the

j +