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Small Computer System Interface (SCSI) was the most common
interface used on legacy enterprise-class rotating hard
drives. While traditional SCSI is a parallel interface,
the trend in the storage industry is to serial these interfaces;
thus were born Serial-Attached SCSI (SAS) and Serial ATA
(SATA).
When the SCSI Trade Association introduced the SAS
standard, it was designed to meet the ever-demanding
needs of enterprise storage for high performance, high
reliability and high manageability. SATA was designed
to be the replacement drive interface for the high-volume
desktop and mobile markets.
Both SATA and SAS use the same physical and electrical
interface, and therefore, SATA drives can be physically
connected to SAS host controllers. Because of additional
command support, SATA host controllers will not support
SAS devices. The three software protocols that can run
on top of this interface are:
• Serial SCSI Protocol (SSP) - supports
SAS drives
• SATA Tunneling Protocol (STP) - supports
SATA drives
• Serial Management Protocol (SMP) -
supports SAS expanders
The SAS standard currently supports up to 3Gbit/sec
data transfer speeds, with future rates planned for
6Gbit/sec and even 12Gbit/sec at the end of this decade.
Key end-user benefits of the standard include an enterprise-class
command set, investment protection in compatible SCSI
software and middleware, and the choice of direct-attach
storage devices (SAS or SATA). In addition, longer cabling
distances, smaller form factors and greater ease of
device addressing will all lead to a new level of flexibility.
Since SAS is based on the foundation of the industry-leading
SCSI specification, it will satisfy users' needs for
continuity in mission-critical applications. |
