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a name synonymous with SCSI Storage, offer a complete range of Host Bus Adaptors including Advanced Hardware Raid Host Bus Adaptors for Today’s Storage requirements |
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SCSI |
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SAS - Serial Attached SCSI |
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SATA - Serial Attached ATA |
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SAS & SATA Internal Housings |
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SAS & SATA Cabling |
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| www.adaptec.com |
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Step Up to SAS for Server Storage
Administrators are often faced with choosing between a newer, more exciting technology or going with an existing, proven one. When it comes to server storage, the choice today is between the Serial ATA (SATA) hard drives and storage devices based on Serial Attached SCSI interface (SAS). Read more...
SAS-Power and Simplicity Becomes One
After months of speculation and anticipation, Serial Attached SCSI (SAS) storage solutions are now entering the market in force. Given its unparalleled blend of performance, scalability and flexibility, it should come as no surprise that SAS is quickly making converts among IT professionals throughout the enterprise. Read more...
Step Up to SAS for Server Storage By Mike Micheletti
Administrators are often faced with choosing between a newer, more exciting technology or going with an existing, proven one. When it comes to server storage, the choice today is between the Serial ATA (SATA) hard drives and storage devices based on the Serial Attached SCSI interface (SAS).
SAS has become the next evolution of SCSI and significantly expands on the capabilities of its parallel predecessor. SATA has effectively replaced the ATA/Integrated Drive Electronics (IDE) standard that was used for years in desktop hard drives and CD/DVD drives. SATA drives have always been inexpensive and easy to work with, but they have also lagged behind SAS drives in terms of performance.
Serial Attached SCSI leverages years of proven SCSI functionality to deliver a storage architecture designed for server applications. SAS technology offers many features not found in SATA or parallel SCSI, such as drive addressability up to 16,000 devices per initiator. In addition to SAS' impressive scalability, lower latency, lower command overheads and faster access times, there are other features that help SAS outperform Serial ATA in server applications:
SAS drives are built for higher duty cycles. SAS drives feature duty cycles of up to 80% which defines the percentage of time the device is rated for servicing I/O requests. Higher duty cycles allow SAS drives to stand up to more demanding data access patterns within the server subsystem. In general, SATA drives are considered desktop-class drives and are not rated above 20% duty cycles.
SATA's command standard isn't enterprise-class. SAS uses a method of optimizing data called command queuing, which allows the controller to retrieve data from the drive in the best possible order. On a server, where there may be dozens (if not hundreds) of concurrent data requests, command queuing can dramatically improve transaction-processing performance. The SATA implementation of command queuing does not offer the same capabilities as SAS, including support for expediting higher priority commands (immediate bit).
SAS architecture can support SATA drives. SAS backplanes and host bus adapters (HBAs) are fully compatible with Serial ATA (SATA) drives, giving unparalleled freedom to choose the optimal solution for a given application. The flexibility of using SATA drives, to provide a high capacity and low cost-per-gigabyte storage for near-line applications, is a plus for SAS.
SATA uses the CPU for managing data flow; SAS doesn't. SATA relies on using the CPU for managing its data flow, another legacy inheritance from the ATA/IDE standard. SAS controllers offload the management of data flow to the controller's own dedicated hardware, which means faster overall throughput. While the amount of CPU load that SATA imposes on the system is nowhere near what it used to be in the older ATA/IDE standards, there is still the overhead required to go to and from the CPU -- and that's CPU power and bus bandwidth best devoted to other things.
SAS Drives support dual porting Serial Attached SCSI's small connector supports full dual-port connections on 2.5-inch hard disk drives, a feature previously found only on larger 3.5-inch Fibre Channel disk drives. Dual-port connections are important for mission critical applications that require redundant pathways to important data.
In short, serial ATA is best for simple, single-disk servers and desktop configurations. The SAS architecture provides a convenient way to incorporate SATA drives when performance and reliability requirements are less stringent. But for enterprise-class server applications, SAS drives will considerably outperform SATA drives due to the fact that the interface is Full Duplex rather than Half Duplex. SAS devices also have lower latency, lower command overheads, faster access times, better command queuing and offer higher duty cycles than SATA.
Please visit the following website for more information: http://www.serialstoragewire.com/Articles/2006_07/sysinsights18.html
For more information on Adaptec Snap Products, please visit: http://www.adaptec.com/en-US/products/sas/
SAS: Power and Simplicity Become One By Bill Schilling and Kent Bransford
After months of speculation and anticipation, Serial Attached SCSI (SAS) storage solutions are now entering the marketplace in force. Given its unparalleled blend of performance, scalability and flexibility, it should come as no surprise that SAS is quickly making converts among IT professionals throughout the enterprise.
Yet some storage managers have been hesitant to adopt SAS, wary of the connection challenges this powerful new serial interface might entail. Having invested years of sweat equity to master the idiosyncrasies of parallel SCSI, they are understandably reluctant to risk a similarly steep learning curve with SAS.
Happily, SAS was specifically designed with a vastly more straightforward and robust connection architecture than parallel SCSI. Gone are the tedious shared bus issues (SCSI ID settings, drive termination, total cable length constraints, etc.) that plague parallel SCSI storage environments; SAS banishes such concerns with the elegant simplicity of point-to-point architecture.
Easier is Better
Point-to-point cabling provides a discrete, dedicated signal path for every SAS device attached. Not only does this boost performance (each attached device is always immediately available on its dedicated bus, minimizing latency), it makes connecting SAS drives a remarkably uncomplicated and intuitive process.
As can be seen in Figure 1, the power and data connectors on a SAS drive are compact and easily accessible. Note the dual data ports; see Figure 4 for the significant benefits this arrangement enables. (Graphics copyrighted by SCSI Trade Association, courtesy of Molex.)
Figure 1
In its most basic form, SAS connectivity entails a single SATA-style SAS cable for each drive, linking to a matching SAS port on the host computer. Figure 2 illustrates cables that are attached to panel-mounted connectors, as well as cables connected directly to the drives. (Drive power is typically handled by a pigtail terminated with a four-pin connector.)
Figure 2
For many IT professionals, the simple type of setup shown in Figure 3 will be all they need to consider. SAS host bus adapters (HBAs) are theoretically capable of carrying dozens of connectors, but in practice most popular HBAs will feature either four or eight SAS ports. Thus an eight-port HBA can directly connect up to eight SAS drives, each port cabled to its respective SAS drive.
Figure 3
As noted earlier, the dual-port drive architecture of SAS provides compelling advantages. Figure 4 illustrates how the extra port on a SAS drive can be connected via a dual-port cable to ensure high availability and greater uptime. If one SAS host controller fails, the extra data port can maintain uninterrupted communication with the second controller. In addition, these two ports can be combined into a single "wide port" for even higher throughput.
Figure 4
And SAS flexibility doesn't stop there. Small form factor (SFF) "multilane" host connectors can be used to provide multiple-drive connections in a more space-efficient design. As shown in Figure 5, four separate SATA-style SAS ports on the host controller have been replaced by a single SAS 4i multilane connector.
Figure 5
Conclusion
As IT managers face increasing pressure to cut storage costs, the prospect of deploying a new and unfamiliar storage interface may be daunting. Will it prove to be so time consuming and labor intensive to manage that any technical advantages it may offer are negated?
From the outset SAS was architected to deliver unprecedented ease of use while incorporating the most up-to-date serial technologies available. The result is a uniquely accessible blend of performance, scalability and flexibility. Rewriting the rules for enterprise storage value, SAS is simply better.
Please visit the following website for more information: http://www.serialstoragewire.com/Articles/2006_07/feature18.html
For more information on Adaptec SAS Products, please visit: http://www.adaptec.com/en-US/products/sas/
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