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FDU1
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Re: 【微博用户提问分享】SAS2.0和SATA3.0的技术对比

参考http://en.wikipedia.org/wiki/Serial_attached_SCSI#Comparison_with_SATA 它们的技术区别如下:

 

  • Systems identify SATA devices by their port number connected to the host bus adapter, while SAS devices are uniquely identified by their World Wide Name (WWN).
  • SAS protocol provides for multiple initiators in a SAS domain, while SATA has no analogous provision.
  • Most SAS drives provide tagged command queuing, while most newer SATA drives provide native command queuing, each of which has its pros and cons.
  • SATA uses the ATA command set; SAS uses the SCSI command set. Basic ATA has commands only for direct-access storage. However SCSI commands may be tunneled through ATA for devices such as CD/DVD drives.
  • SAS hardware allows multipath I/O to devices while SATA (prior to SATA 3Gb/s) does not. Per specification, SATA 3Gb/s makes use of port multipliers to achieve port expansion. Some port multiplier manufacturers have implemented multipath I/O using port multiplier hardware.
  • SATA is marketed as a general-purpose successor to parallel ATA and has become common in the consumer market, whereas the more-expensive SAS targets critical server applications.
  • SAS error-recovery and error-reporting use SCSI commands which have more functionality than the ATA SMART commands used by SATA drives.
  • SAS uses higher signaling voltages (800–1600 mV TX, 275–1600 mV RX) than SATA (400–600 mV TX, 325–600 mV RX). The higher voltage offers (among other features) the ability to use SAS in server backplanes.
  • Because of its higher signaling voltages, SAS can use cables up to 10 m (33 ft) long, SATA has a cable-length limit of 1 m (3 ft) or 2 m (6.6 ft) for eSATA.

另外在物理规格上,SAS最重要的是支持dual-ported,一块SAS盘可以连接两个SAS HBA实现更高的可用性:

dual_port_cable.jpg

还有一点就是,目前SATA和SAS的平均无故障时间 (MTBF)已经很接近了,但误码率(BER) SATA要比SAS高10倍(10^15分之一 vs 10^16分之一),从可靠度来讲SAS比SATA高许多,因此通常建议由SATA或NL-SAS组成的RAID group尽可能采用RAID 6而不要使用RAID 5。

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