How RAID Controllers Evolved
In the pre-SATA times, companies such as 3Ware, Highpoint and Promise realized that RAID outside the professional SCSI world made a lot of sense -especially when using inexpensive ATA hard drives. Highpoint and Promise were the first companies to offer add-on controller chips, which motherboard makers integrated into their premium consumer products. But they also offered PCI expansion cards to enable ATA RAID on entry-level servers. Although performance and reliability by no means was at the level of professional components, it still made sense for small business customers to compare cost and features. It has been absolutely possible to setup a secondary server using cheap ATA components and simple RAID controllers, which only support RAID 1.
With the introduction of SAS and SATA, both the mainstream and the professional drives share the same infrastructure (though it’s not possible to run a SAS hard drive on a SATA controller). The result is a tremendous increase in flexibility for business customers, as they don’t have to decide between inexpensive ATA solutions or sophisticated professional products. All you need is a decent RAID controller, and you’ll be able to run both. Most RAID controllers will work on all popular operating systems including, of course, Windows and Linux and sometimes on Solaris and Novell Netware, while they increasingly can accommodate Mac operating systems. It also doesn’t matter whether you use a client or a server OS; many cards will run on both.
RAID controller cards were offered for all major bus standards starting with EISA (32 bit, 8 MHz) and VESA Local Bus (32 bit and 33+ MHz), continuing via PCI (32 bit, 33 MHz) all the way to PCI-X (64 bit, up to 266 MHz), which is still widely available today. The serial PCI Express bus is now taking over almost all market segments, because it offers its maximum bandwidth of up to 4 GB/s upstream and downstream (PCI Express 1.x standards x16 lanes) for each device. In addition, higher integration and multi-lane cables allow for smaller dimensions of the controller cards and hence the creation of more powerful low-level cards. These fit into 2U rackmount servers and hence allow for the creation of dedicated storage servers utilizing very little space. Also, internal and external connectors are available for SAS; in the case of SATA you can either utilize SAS hardware or try eSATA, which is only configured for single drives.
More sophisticated manufacturing technologies do not only allow for higher memory densities and faster processors, but also for faster XOR engines for parity-enabled RAID controllers to accelerate performance. The feature sets of the cards we reviewed are often inherited from software and management solutions that were originally designed for SCSI RAID controllers. If you’re familiar with them, you’ll easily be able to handle a Unified Serial RAID controller for SAS and SATA.