Conventional PCI became the standard IO bus during the 1990s, and was followed by newer versions such as PCI-x and PCI-x 2. However, despite these enhancements, processors demanded even higher IO throughput.
PCI Express (PCIe) was developed as a serial connection to provide scalable point-to-point connections while maintaining software compatibility with conventional PCI.

Since then PCIe rapidly become the defacto standard backplane bus architecture, achieving nearly 100% acceptance in desktop and laptop PCs. Over 60 form-factors have been defined using PCIe as the backplane bus architecture.
It later became clear that the PCIe bus could be separated from the used in an external environment as a means of addressing peripheral devices without necessitating performance detracting protocol conversions and timing delays.
On 7 February 2007 the Peripheral Component Interconnect Special Interest Group approved the standard for PCIe over Cable. (PCI-SIG: http://www.pcisig.com)

PCIe as a single hosted DAS solution has many options and advantages over the other available technologies. The obvious performance and cost benefits should make this technology high on anyone selection list. The other options include front end expansion using a PCIe switch and back-end expansion via a SAS bus to JBODs or further RAID systems.