Abstract: In a multimedia data stream system, deterministic response is provided by multimedia servers for VCR client commands, thereby ensuring the commands execute within a predetermined deterministic window of a base response time +/- a jitter j. A command is timestamped and blocked until within the determinstic response window, and then released from a queue. An I/O then issues to a decoder card in a time period less than 2j. Threads processing these commands run at elevated priority. Non-deterministic commands default to the high priority but priority of a thread receiving such a command is lowered before processing. The response time jitter is bound by high priority commands by issuing only non-blocking I/Os and limiting the number of concurrent SCSI bus commands.

Abstract: In order to increase the number of datastreams provided by a multimedia system, a cluster of clusters of multimedia A/V server subsystems is provided. Each cluster in turn is comprised of a plurality of A/V servers, a shared loop architecture plurality of data storage devices interconnected to the A/V servers whereby any storage device is substantially equally accessible by any of the servers in the cluster; and a highly available control server subsystem interconnected to the A/V servers and the data storage devices for controlling the A/V servers and the data storage devices. Each of the clusters is interconnected to a high speed switch for delivery of datastreams from the cluster to the end user. One of the control server subsystems also serves as a master control server assigning a request for a datastream to one of the clusters.

Abstract: Response time jitter for high priority commands in a multimedia datastreaming system is bounded by issuing only non-blocking I/Os and by limiting the number of concurrent SCSI bus commands. A device driver in the system bounds the maximum time a VCR command must wait after it is released from a VCR queue by limiting the number of I/Os on the bus to a predetermined number functionally related to the magnitude of jitter permitted in the deterministic response requirement, and the time required for each data I/O to be issued to the decoder card. The number is such that the I/Os may issue within the jitter time with enough time remaining for issuance of a high priority VCR I/O. By limiting the I/Os to a predetermined number, the I/Os issued are constrained to be non-blocking to avoid hanging the I/O scheduler when a deterministic hhigh priority command arrives.