Inter-processor data transfer via SCSI-2

Summary form only given. The data acquisition system for the STAR experiment at the Brookhaven National Laboratory will readout data from several large detectors, and, following event building, data will be transmitted to a remote data storage facility. The architecture chosen requires data transmission from the STAR master VME crate to a Sun E450 which will control onward transmission via a 2 km Gigabit ethernet link to the HPSS storage facility. The E450 will provide sufficient buffering to handle short- and long-term disruption of the link and storage facility. Transmission from the VME crate to the E450 is performed via a SCSI-2 link. This method has been chosen because of its simplicity and cost-effectiveness. Since events are fragmented in memory, the scatter-gather mode of the SCSI chip provides a seamless method of data transfer. The technique requires configuring the SCSI chip on board the Motorola MVME2604 to emulate a tape drive. This “virtual” tape is read by a process on the Sun. Transfers of 20 MHz have been achieved with ~2% utilization of the VME CPU. The same transfer using Gigabit ethernet would utilize 3 CPUs