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
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