While hardware RAID controllers werehave been available for a long time, they alwaysinitially required expensive [[Parallel SCSI]] hard drives and aimed at the server and high-end computing market. SCSI technology advantages include allowing up to 15 devices on one bus, independent data transfers, [[hot-swapping]], much higher [[MTBF]].
Around 1997, with the introduction of [[Atapi|ATAPI-4]] (and thus the [[Direct memory accessUDMA|Ultra-DMA-Mode 0]], which enabled fast data- transfers with less [[CPU]] utilization) the first ATA RAID controllers were introduced as PCI expansion cards. Those RAID systems made their way to the consumer market, where thefor users wantedwanting the fault-tolerance of RAID without investing in expensive SCSI drives.
ATAFast consumer drives make it possible to build RAID systems at lower cost than with SCSI, but most ATA RAID controllers lack a dedicated buffer or high-performance XOR hardware for parity calculation. As a result, ATA RAID performs relatively poorly compared to most SCSI RAID controllers. Additionally, data safety suffers if there is no [[Battery (electricity)|battery]] backup to finish writes interrupted by a power outage.
