Seagate 15K.2 Inflection Point - The New Era of Serial Attached SCSI - Page 6

SCSI Inflection Point: Standardizing on Serial Attached SCSI (SAS) has established itself as a highly effective means to drive high-speed signals over long cables while minimizing vulnerability to environmental noise (for example, RFI). Utilizing the differential signal between a pair of conductors promotes immunity to common-mode noise, while the low voltages made possible by this approach enable increased signal speeds that would be unattainable at higher voltage levels. While Ultra320 SCSI requires an imposing 32 signal conductors (two for each of the 16 data paths) to implement LVD signaling, SAS needs only four. Fewer conductors require less power to drive the signals, are far less susceptible to crosstalk, and result in much smaller and less intrusive cabling. Full-Duplex, Dual-Port Design Full-duplex operation doubles effective throughput by enabling simultaneous signal transfers in both directions. To provide for high availability and greater uptime, dual data ports ensure that if one SAS host controller fails, the extra data port can maintain uninterrupted communication with a second controller. In addition, these two ports can be combined into a single, wide port for even higher throughput. Enhanced Scalability SAS was specifically designed to maximize the ease with which drives can be added to boost both capacity and throughput. In concert with SAS's point-to-point architecture (see above), high-speed switches known as expanders enable quick aggregation of many drives, allowing a single SAS domain to contain up to 16,384 devices (128 maximum SAS devices per edge expander x 128 maximum edge expanders per fan-out expander) without performance degradation. And multiple SCSI domains can easily be interconnected to achieve exceptional levels of data availability. cost-effective for lighter-duty use, such as nearline and backup/restore storage. When storage priorities shift, it's a simple matter to alter the drive mix by plugging in additional SAS or SATA drives. Furthermore, SAS/SATA compatibility will significantly reduce the cost and complexity of the data center by minimizing the number of individual components that must be qualified, inventoried and maintained. Such component rationalization also places fewer demands on management resources and support personnel. Longer Effective Cable Length A maximum cable length of eight meters (approximately 25 feet) facilitates connections to both direct-attached storage and discrete storage arrays deployed near the server. SAS's point-topoint architecture enables this maximum cable length to be used for each dedicated connection between two devices, thus allowing thousands of feet of cabling in a SAS domain. The maximum length allowed is not additive of all connections, as it is on a parallel SCSI bus. Compact Cabling/Connectors SAS connectors and cables are far smaller than comparable parallel SCSI pieces; this simplifies cable routing, saves space and improves airflow/ cooling in system or storage cabinets, and ensures SAS connectors easily fit on small form factor devices. Hot Pluggable/Hot Swappable SAS's hot plug capability enables drive swapping without system shutdown, thus ensuring uninterrupted data availability. Blind mate connectors (designed to positively lock in place, eliminating the need to visually verify a connection is properly seated) ease connection in cramped or inaccessible installations. Worldwide Unique Device ID Compatibility with SATA By ensuring Serial Attached SCSI cables/ connectors, backplanes, expanders and host bus adapters (HBAs) are fully compatible with Serial ATA drives, SAS ensures the freedom to seamlessly adapt as storage needs inevitably change and evolve. SAS disk drives are clearly the best choice for mission-critical enterprise Every SAS port and expander has a worldwide unique 64-bit SAS address (derived from the same namespace as the Fibre Channel Port Name), burned into the device's firmware at the time of manufacture. This eliminates the need to manually set SCSI ID numbers via jumpers or switches, as well as any possibility of device ID conflicts when installing/moving SCSI devices or expanders. use where transactional/online performance and 6 reliability are crucial, while SATA disk drives are