30
6Gb/s SAS: Destined for Growth in
External Storage
OGY
Serial Attached SCSI (SAS) has made significant strides over the past
several years as the replacement for parallel SCSI, which has been the
storage interface of choice in the server market, writes Harry Mason,
TECHNOL
Director Industry Marketing, LSI Corporation.
In fact, SAS is now the addressability beyond parallel topologies across multiple
dominant storage interface SCSI capabilities, with the vendors, while increasing the
SAS
offered by server vendors ability to connect multiple number of supported zones
worldwide, overtaking SCSI servers and thousands of from 128 to 256.
shipments in 2007. With its storage devices. Scalability at
ability to support both SAS this level often requires that Unforeseen growth in
and SATA drives, SAS is the storage devices and/or datacentre capacity requires a
making headway as the subsystems be consistently flexible architecture. Since
interface of choice for external assigned or zoned to operate SAS was primarily intended as
storage in both JBODs and with multiple hosts in a parallel SCSI replacement, it
external RAID subsystems. virtualised server sometimes lacked an efficient
SAS is also penetrating a deployments. This ability to means to initialise large disk
segment that until now has assign various operating drive configurations. By
primarily been the domain of domains for both shared and shifting more of the SAS
Fibre Channel, the host separate pools of storage is topology discovery process
connection of those external accomplished through a from the host controller to the
storage systems that are capability referred to as SAS expander, and providing
already adopting SAS. expander zoning. added flexible table-to-table
The 3Gb/s SAS expander routing, 6Gb/s SAS now
Coinciding with the increased vendors had implemented reduces messaging during
interest in, and adoption of zoning schemes that were, in discovery thus reducing
SAS, is the need to address some cases, vendor-unique initialisation time. This
emerging market trends such and not necessarily efficiency gives system
as virtualisation, improved compatible with the zoning builders the functionality to
scalability, better storage schemes of other vendors. discover, initialise and scale
manageability and more Emerging interface with increasing capacity
robust data integrity. As such, capabilities are often demands that drive tiered
the SCSI Trade Association introduced into the market in solutions.
(STA) and ANSI T10 Technical this manner and when
Committee set out to define sufficiently supported, Higher Performance,
new features in the SAS-2 eventually make their way Longer Cables
specification to better into the standard. Expander A key element in the
position 6Gb/s SAS for zoning was standardised in progression towards 6Gb/s
external storage connectivity. the SAS-2 technical SAS is the desire to preserve
specification and adopted the distance and compatibility
New Expander as a 6Gb/s SAS expander offered by 3Gb/s SAS
Capabilities for requirement. This standardised environments while doubling
Enterprise Scalability zoning improves SAS’ ability the data transfer rate. As SAS
SAS today supports to effectively support complex finds its way into enterprise
OCT 09 WWW.SNS-UK.CO.UK
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