Friday, October 14, 2011

Why you should rethink SAS over SATA


SAS drives are dual ported, which means that they can be controlled by 2 controlers at the same time, and there are 2 paths to the data. And not only are there 2 paths but you can send and receive data at the same time on both paths, this is called called Full Duplex. 

SATA drives are single ported and can only be controlled by 1 controller.To have 2 data paths to the SATA drive you need a Mux board or port multiplier. Even then the data can only be sent in one direction at a time, and only 1 of the 2 ports can be used at any given time, and then the data can only flow in one directionat a time. 

SAS uses Tagged Command Queuing(TCQ) is a technology that allows sending multiple read and write requests to a hard drive simultaneously.  

SATA uses Native Command Queuing, (NCQ) is a technology designed to increase performance of SATA hard disks. It can do this under certain situations by allowing the individual hard disk to internally optimize the order in which it executes the read and write requests it recieved. However the current (as of 2004) technology actually slows down hard drive access in certain applications, like game and sequential read and writes, because of the added latency induced by NCQ logic.  

SAS drives have the intelligence to manage their own media and remap bad blocks on the fly. SATA drives only know there is a error if data is written or try to read from an affected area of the disk. 

SAS error recovery and reporting utilize SCSI commands which have more functionality the the ATA SMART commands used by SATA drives. 

SAS drives also handle rotational vibration better than SATA drives. SATA drives need to recalibrate to stay on track, and that decreases performance.  

SAS drives are now more competitively priced. They are typically less expensive once Mux Boards are added to SATA drives,


SAS Functionalty and Features

  • Variable Sector Size
  • Multiple Host Support
  • Full SCSI Comannd Set
  • Independent Port Clocking
  • Multi Host Command Queuing
  • Mode Pages


SAS drives out perfom SATA Nearline Drives

  • 25% improvement in sequential reads
  • 140% improvement in sequential writes
  • 15% improvemnet in random reads
  • 20% improvement in random writes
Contact NavigateStorage or call 978-318-9000

No comments: