Serial Storage Wire » Compatibility » Migration » Reliability » SAS » Scalability
By Paul Vogt, Director of Product Marketing,
The flexibility of Serial Attached SCSI (SAS) allows it to be used as a universal connectivity standard for a wide range of business needs. In addition to its role as a replacement for parallel SCSI, SAS now offers the ability to reduce the cost of servers and storage networks, to create tiered solutions that weren't possible before, and to provide investment protection for SATA installations. While SAS performance and scalability generate a majority of the media attention, it could be the flexibility that SAS brings to storage subsystems that creates the most value for your business.
SAS as a parallel SCSI replacement
SAS maintains support for the proven SCSI command set while offering much better performance, scalability, and availability. Stability and reliability have made parallel SCSI the standard in storage connectivity for twenty five years. SAS offers compatibility with this command set while overcoming the physical limitations of parallel SCSI. Now with SAS, it is possible to take advantage of dual-port drives, redundant connections, failover support and scalability up to 128 attached devices and over 16,000 addressable devices. Performance at 3Gb/s per port can be aggregated into wide-port connection bandwidth.
By design, SAS can co-exist in an existing SCSI environment, protecting previous SCSI investments. Users are expanding SCSI installations by adding a SAS controller into the server and attaching their choice of high-performance, high-reliability SAS drives or high-capacity SATA drives.
Creating lower cost fault-tolerant servers
SAS is an ideal solution for the creation of fault-tolerant IOP servers. It provides the very high reliability required to run 24 hours a day, supporting mission-critical applications with no data loss. SAS features such as point-to-point connectivity and dual-port drives allow for cable and port redundancy for fault tolerance not present in parallel SCSI. Previously, the creation of these no-fail servers required the use of expensive Fibre Channel connections and disks.
To further decrease the possibility of data loss, SAS motherboards can be combined with RAID in RAID-on-Motherboard solutions, which provide data protection at a price significantly below the price of adding a separate RAID card.
Transitioning to a smaller form factor product does not mean users must sacrifice on reliability. In fact, reliability has improved with the latest generation of SAS hard disk drives to 1.4M hours mean-time-between-failure (MTBF). Additionally, lower power consumption means less heat is generated within the system. This can translate to fewer cooling requirements (less money spent on fans and cooling systems) being needed overall.
Creating a SAS infrastructure for large-capacity SATA drives
Users of high-capacity SATA drives can also take advantage of SAS to get more from their SATA investment. Combining a SAS controller with SATA drives allows the connection of up to 128 individual drives or storage arrays with SATA drives, for truly high-volume storage. With the 1:1 port-to-connectivity relationship of a SATA controller, scalability is limited to four, eight, or 16 connections. SAS also provides a reliable connection to an external JBOD filled with SATA drives if the application requires large data capacity.
Integrating SAS and SATA drives for tiered storage and ILM
The ability of SAS controllers to connect to SAS drives along with SATA drives enables cost-effective, easily-managed tiered storage that simplifies information life-cycle management (ILM). As shown in the image below, one controller connects primary SAS storage and secondary SATA storage in a single solution. It provides massive scalability as data grows and makes re-allocating storage as simple as swapping disks.
Centralizing storage using zoning for blade implementations
SAS brings the flexibility to connect SAS and SATA drives to the increasingly popular blade server environments. Through the use of expanders, SAS allows the connection of multiple hosts to multiple targets. However, in cluster and blade implementations, this means that all of the servers can see all of the data in the shared storage resource. Of course, not all servers need to be able to access all the data. In Ethernet and Fibre Channel infrastructures, switches provide zoning that allow a blade to see only the data appropriate to it. Emerging SAS switch products will provide this zoning feature for SAS blade servers. The zoning feature is currently being defined for inclusion in the SAS-2 draft standard.
Enabling a low-cost, high-performance local SAN
Small and mid-size businesses can forego the cost and complexity of building an expensive SAN by leveraging their SAS components into a storage network inside the rack. SAS expanders and RAID controllers enable the connection of many devices, and the wide-port feature (which aggregates ports for total bandwidth) works well for performance-intensive applications such as video editing and document imaging. SAS disks provide high-end reliability and performance without the high cost of more complex storage networking implementations.
With its many possible usesparticularly its ability to integrate with popular SATA drivesSAS provides a single, highly-flexible standard. It offers unique cost-effectiveness to both business users (with a variety of needs) and solution providers (who meet a range of customer needs from basic connectivity to networked storage configurations). IT managers would do well to see where they can start incorporating SAS into their storage environments today, in an effort to extend the life and flexibility of their storage solutions well into tomorrow.
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