By LSI Logic
Today’s
enterprise storage landscape is dominated by products using
the SCSI interface. With close to 90 percent market share
of all enterprise-class storage systems, SCSI is clearly the
most widely deployed, high-availability enterprise storage
I/O technology in use. Over its twenty-year history SCSI has
evolved dramatically, currently offering a parallel interface
that supports data rates of up to 320 Mbytes/sec. Throughout
those two decades SCSI has remained a compelling interface,
to system designers and IT professionals alike, because it
offers three critical advantages: high performance, exceptional
flexibility with the ability to connect to multiple peripherals,
and proven backward compatibility.
As with
the introduction of any new technology, the migration from
parallel SCSI to Serial Attached SCSI (SAS) requires OEMs
give due consideration to the implementation, deployment,
and maintenance of new SAS-based solutions. That said, transitioning
from a parallel architecture to a serial, point-to-point model
may prove less daunting than some expect, while providing
investment protection well into the future.
3Gb/s
Is Just the Beginning
From the very beginning, Serial Attached SCSI was designed
to support servers with either direct-attached storage or
storage arrays in close proximity. Furthermore, the SAS standard
calls for interconnects that can serve both SAN and NAS devices.
While the initial release of SAS specifies a 3Gb/s interconnect
bandwidth, a technology roadmap laid out by the SCSI Trade
Association will soon migrate this new high-performance technology
to transfer rates of 6Gb/s and 12Gb/s. As such, designing
3Gb/s systems today lays the groundwork for future compatibility
with the higher data rates of tomorrow.
Interface
Compatibility
A powerful (indeed, unique) advantage of Serial Attached
SCSI is its ability to support both SAS and SATA disk drives,
thereby allowing system developers to design a platform (whether
server, drive enclosure, etc.) that can accept either drive
interface as needed. Ultimately, OEMs will be able to service
two market/storage application segments and enhance customer
choice for storage solutions with a single SAS design: higher-performance,
transactional data requirements with SAS disk drives, and
lower-cost, higher-capacity reference data needs with SATA
disk drives.
Leveraging
SCSI
Another compelling advantage of Serial Attached SCSI
is its compatibility with the SCSI command set used in parallel
SCSI. This mature, proven command set has been developed and
refined over the past two decades. Today’s system developers
struggle to meet the demand for greater capacity, performance
and scalability while still maintaining compatibility with
the vast installed base of legacy storage systems. By leveraging
the SCSI command set, SAS gives IT professionals software
continuity and preservation of the system-level applications
previously used in parallel SCSI environments.
At the
operating system driver level, the required changes for SAS
are minor, primarily involving device initialization and discovery.
But there are major benefits to SAS’s SCSI compatibility—IT
professionals can leverage their deep knowledge of SCSI to
address new storage applications, ranging from direct-attached
storage to NAS and SAN environments. Moreover, the ubiquitous
SCSI protocol is also embedded in next-generation Fibre Channel,
iSCSI and InfiniBand technologies.
Conclusion
It’s a goal every IT department shares: Seamlessly
integrating enterprise storage systems while ensuring cross-platform
functionality, high reliability and cost-efficient management.
To achieve this goal requires storage technologies whose system
software masks the complexity of integrating old and new systems,
while still minimizing deployment costs. Serial Attached SCSI
enables IT departments to leverage their substantial investments
in legacy SCSI technology, while intermixing higher-performance
SAS disk drives with lower-cost SATA disk drives for high-capacity
needs. In doing so, SAS provides IT professionals with unmatched
deployment flexibility, performance and reliability at minimum
cost.
