Home | Business News | Browse by Publication | C | Computer Technology Review

The challenges of testing SATA and SAS; Part 2: primitives and frames.

Article Excerpt
Serial ATA (SATA) and Serial Attached SCSI (SAS) are quickly replacing their parallel counterparts. SATA is already the undisputed heir to the ATA throne, and SAS is poised to replace SCSI by offering an economical roadmap to higher bandwidth, while providing backward compatibility with SATA.

[FIGURE 1 OMITTED]

Most SAS hosts can connect to SATA drives directly using the native SATA protocol, sacrificing the advanced features of SAS and limiting the connection to a single drive. SAS hosts can also connect to SATA drives through a SAS Expander using the SATA Tunneled Protocol, which encapsulates SATA frames within the SAS addressing frames. This allows a SAS host to connect to multiple SAS and SATA drives, combining the multi-drive capabilities of SAS with the low cost of SATA.

Analyzing the traffic on a mixed SAS/SATA bus is best done with a SAS analyzer that supports both protocols, although for the native SATA connections a SATA analyzer will work fine. Figure 1 shows where in a mixed SAS/SATA system a SAS analyzer is required, and where a SATA analyzer will suffice.

SATA and SAS: By the Numbers

With all of its advanced features. SAS is significantly more complex than SATA. SAS devices will be more expensive but the price is easy to justify in an enterprise storage environment where increased versatility and reliability (MTBF) are critical. The Table provides a SATA/SAS comparison of the additional feature complexity that comes with SAS.

Handshaking on a Serial Bus

While individual signals were often used for handshaking and signaling special events on Parallel ATA and SCSI, on the new...