An Analysis of PCI Bus Utilization by Zero Channel RAID

Zero Channel Raid (ZCR) is intended to be a low-cost, low-profile, entry-level RAID solution ideal for use in 1U and 2U servers that employ a relatively small number of drives due to space constraints. Unlike N-channel RAID controllers that integrate the RAID functionality and transport modules on a single board, ZCR controllers provide transport protocol independence by decoupling these modules. This decoupled architecture offers several benefits. It reduces the cost of incorporating RAID onto platforms whose motherboards already feature embedded SCSI or ATA chips. It also enables the ZCR controller to support drives of varying interfaces and operate with future generations of motherboards with more advanced embedded transport chips using updated firmware. However, the effect of ZCR controllers on system performance due to the I/O overhead they introduce on the system PCI bus may be a concern since the bus is used as the communication path between a ZCR controller and the transport chip. In contrast, this communication path in traditional N-channel RAID is an autonomous bus that is local to the controller. This paper addresses this concern by quantitatively analyzing the I/O overhead introduced by a ZCR controller on the system PCI bus and proving that it is not significant enough to negatively impact performance.

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