Seagate ST3750330NS Seagate Barracuda ES.2 SAS Hard Drives and LSI MegaRAID SA - Page 3

Why Choose Tier 2 SAS over Enterprise SATA for Nearline Applications With the release of the Seagate ES.2 SAS drives, Nearline applications can now enjoy enterprise peace of mind without the enterprise cost. Until now, organizations rightly chose to use Enterprise SATA drives due to their combination of affordability and increased reliability over desktop drives. However, with the price of Seagate's Tier 2 SAS drive at pennies more per gigabyte than the comparable Enterprise SATA offering, users no longer have to settle for "good enough". Seagate Tier 2 ES.2 SAS drives offer many of the features and functionality of the Tier 1 SAS drives, such as Seagate's Savvio and Cheetah. These features include dual port, full duplex, concurrent active channels, robust command queuing and superior error detection and correction. The combination of full duplex, dual port, concurrent active channels and SAS command queuing, give SAS drives a large performance advantage over Enterprise SATA drives. Full duplex supports data reads and writes in both directions simultaneously, which greatly increases throughput. This inherently provides better performance than Enterprise SATA, which only supports half duplex, or the transfer of data in one direction at a time. Dual port provides two redundant paths to every hard drive. This increases availability and reliability by supplying each drive with an alternate path of communication in the case that one path fails. SATA, which is single port, only offers one path to every hard drive. Thus, if this single path of communication fails, there may be data loss and system downtime. SAS hard drives also provide two active (concurrent) channels, which allow data to be transmitted to and from the disk drive on two separate channels. This means that the drive can execute two write commands, two read commands or a write and read command at the same time. With SATA, there is only one active channel, which means you can only have one read or one write at a time. According to Seagate benchmarks, the combination of dual ports and concurrent channels on SAS hard drives yields an average performance increase of 135% over SATA. Another feature of SAS that trumps Enterprise SATA is SAS command queuing. Seagate's Barracuda ES.2 SAS has a clear advantage with two CPUs (vs. one with SATA). Although both SATA and SAS offer command queuing, the 2nd CPU provides smarter and more robust command queuing, thus improving efficiency and performance. Barracuda ES.2 drives offer the benefits of SAS technology at Enterprise SATA pricing. Full Duplex n Transmits in both directions at one time (orange arrows) Dual Port n Two redundant paths to each hard drive (Channel 1 and 2) Two Active Channels Port A n Hard drive can communicate via two channels for; n 2 concurrent Writes or n 2 concurrent Reads or n 1 Write + 1 Read SAS Port B Port A SAS SATA Half Duplex n Transmits in one direction at a time Single Port n Single path to each hard drive (Channel 1 and 2) SATA One Active Channel n Hard drive can communicate through only one channel for; n 1 Write or n 1 Read Seagate Barracuda ES.2 and LSI MegaRAID SAS/SATA Adapters 3