Author: Sam Sawyer
Hitachi GST
The new
serial interfaces, Serial Attached SCSI (SAS) and Serial ATA
(SATA), have been designed to replace their parallel predecessors.
They will support faster data transfer rates and more devices
per controller, as well as reduce the size and complexity
of the cables and connectors (thus enabling smaller, more
densely-packed disk arrays). System builders will also be
able to integrate SAS and SATA hard drives in a single enclosure.
SAS goes
beyond SATA by adding dual porting, full duplex and device
addressing; furthermore, it offers higher reliability, performance
and data availability services, as well as logical SCSI compatibility.
SAS will continue to enhance these and other metrics as the
specification evolves, including increased device support
and longer cabling distances.
SAS
Reliability
For customers requiring the highest levels of reliability
and performance in mission-critical server environments, SAS
hard drives will offer the most reliable and most appropriate
solutions. This is due, in part, to the dual-port attributes
of the SAS interface.
Redundancy
SAS hard drives are designed to withstand the demands of high
duty cycle enterprise storage applications. The dedicated,
point-to-point SAS architecture provides reliable connectivity
and full bandwidth to each drive. Dual porting provides two
separate data paths, allowing for higher levels of performance
and eliminating single points of failure. The support for
redundant connections enabled by the dual port feature is
one of several key differentiators between SAS and SATA drives.
It is one of the reasons that SAS drives are well suited for
use in high-availability enterprise storage environments.
In parallel
architectures, multiple initiators have traditionally been
used to provide hard drive access to multiple hosts and host
bus adapters. The multiple initiator approach, however, can
result in single points of failure that can prevent drive
access.
The dual-port
characteristics of SAS address this challenge by eliminating
single points of failure, enabling the design of high availability
systems. This “full failover” capability, previously
the exclusive domain of Fibre Channel SANs, will positively
enhance the reliability of entry-level direct-attached storage
(DAS) architectures.
Performance
Benefits
Point-to-point SAS architecture eliminates the shared (parallel)
bus bottleneck. In addition, SAS bandwidth can be aggregated
over multiple, low-cost, full-duplex SAS links, allowing data
to be streamed in both directions simultaneously, increasing
data throughput and overall system performance.
SAS also
supports applications such as clustering by allowing dynamic
load balancing. Dynamic load balancing is an application that
distributes the load across multiple controllers and data
paths to increase throughput. Load balancing requires dual-port
SAS drives and multiple initiators.
SAS features
data transfer rates of 3Gb/s with a performance roadmap to
6Gb/s, 12Gb/s and beyond. These interface speeds will deliver
the highest levels of system performance for bandwidth-intensive
applications in direct-attached, networked-attached and networked
storage environments.
For enterprise
customers with stringent reliability, availability and performance
requirements, use of dual-port SAS hard drives will be a major
step forward—and they’ll help the IT staff rest
easy.
