February 2009

In this Issue:

SATA Power Management
Optimum Test Performance for 6Gb/s SATA
SATA-IO Plugfest and Annual Members Meeting: June 8-11
SATA-IO Makes a Splash at Storage Visions

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SATA Power Management

Rising costs of powering and cooling computer systems and storage have caused power management to become an increasingly important issue in all computing markets. In fact, it is now a de facto requirement that system components, such as peripherals and host controllers, support some form of power management. Power management protocols are included in many interface standards, including Serial Attached SCSI and Serial ATA.

To combat significant power consumption, the SATA power management protocol provides the means to place the Physical interface (PHY) into reduced power modes.  However, as portions of the PHY are shut down to conserve power, the SATA device's ability to respond to commands is impacted. The SATA protocol therefore enables the tracking of the power modes of devices and makes allowances for the added latencies required to wake up from reduced power modes.

The SATA specification defines three SATA interface power modes: PHY Ready (PHYRDY), partial and slumber. Partial or Slumber power modes can be initiated by the host or by the SATA peripheral itself, typically after some period of inactivity. The SATA PHY can be awakened or placed back into PHYRDY mode upon receipt of a wake-up signaling sequence from the host.

Greater power savings can be achieved by shutting down portions of a SATA device other than the PHY, such as spinning down the disks in a hard drive. The ATA8-ACS standard describes four modes of power consumption for SATA products: active, idle, standby and sleep. Here again, the tradeoff of increased power savings is a longer initial response time. So spinning down a hard drive should only be done when it is known that the hard drive will not be accessed again for a significant period of time.

Newer desktop PCs also support SATA power management, typically spinning down the hard drive and putting the system into sleep mode after some period of inactivity.  Additionally, storage servers use multiple levels of power management, but because the focus is typically on performance, Sleep mode may not often be used, due to the extended wake up time.

At the high end of the data storage spectrum are MAID systems (Massive Array of Idle Disks), which may consist of hundreds to thousands of hard drives used for storage of reference data that is only occasionally read and very seldom changed. The hard drives in a MAID system spend most of their time in Sleep mode, waking up only when the data is accessed.

When selecting a data storage component such as a hard drive or host controller, the focus has traditionally been on capacity and performance. However, power consumption has become just as important. To ensure that the system power consumption is minimized, power management capabilities such as those provided by SATA are mandatory.

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Optimum Test Performance for 6Gb/s SATA

The introduction of SATA 6 Gb/s will enable large amounts of data to be moved at even faster rates. However, carrying high signals several meters over copper cables tests the limits of signaling technology. At these higher speeds signal integrity becomes a significantly more important design concern for equipment designers and network engineers as tolerances drop to the point where test equipment can adversely affect signal integrity.

Higher frequency signals have increased sensitivity to attenuation and jitter. Over longer distances the higher frequencies tend to attenuate faster than lower ones. The higher frequencies are also more susceptible to jitter while the signal period decreases.

SATA 6 Gb/s standards take a different approach to resolving attenuation and jitter issues. Rather than utilizing de-emphasis and equalization techniques to minimize attenuation and jitter, SATA 6 Gb/s offers a lower-cost link technology for applications that don't require these capabilities.

There are several methods available for connecting test equipment that reduce or compensate for these effects to varying degrees: Analog Passthrough, Digital Retiming and Buffering (or Re-amplifying). Buffered connections reduce the attenuation induced by test equipment by electrically amplifying signals to enable the use of longer cables, providing the best signal integrity.

There are several ways to improve signal integrity. First, co-locating the analyzer, host and device under test simply reduces cable length. Using longer cables increases the attenuation, which is especially true for SATA. Second, using high-quality shielded cables reduces jitter and avoids "phantom" problems. Standard SATA cables have shielding around individual conductors, but not around the cable itself. Using higher quality cable can accelerate development in testing. Finally, it's important to use cables that meet SATA specifications in testing, as inappropriate cables could significantly delay development from integrity issues.

Moving to 6 Gb/s increases the difficulty of maintaining signal integrity between network devices. Many developers will struggle with signal integrity issues that unfortunately will arise from their own carelessness in how they manage their test setups. Those developers and systems engineers who respect the tighter tolerances of operating at 6 Gb/s will find themselves free to accurately identify and resolve protocol system issues more quickly and painlessly.

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Join us for the SATA-IO Plugfest and Annual Members' Meeting: June 8-11

Mark your calendars - the 2009 SATA-IO Plugfest & Interoperability Workshop will be held June 8-12, 2009 in Milipitas, Calif. The event will be held in conjunction with the annual SATA-IO members' meeting, where SATA-IO leadership will provide updates on the status of work within the organization.

This may be the only testing event held in 2009. Don't miss the opportunity to have your products tested!

Stay tuned for additional logistics and registration information in the coming weeks.

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SATA-IO Makes a Splash at Storage Visions

On January 6, 2009, SATA-IO's Marketing Work Group Chair - Conrad Maxwell - presented at the annual Storage Visions Conference, held in conjunction with the International Consumer Electronics Show in Las Vegas. Conrad's presentation, entitled "Smart and Secure Storage", addressed how SATA 6Gb/s technology meets the "need for speed" in today's continuously evolving storage environment.

Speed was a hot topic at Storage Visions, as Solid State Drives and external storage options dominated the conference panels. Conrad's presentation highlighted how the upcoming SATA Revision 3.0 specification fits into the current storage landscape, and helps consumers transmit data quickly and efficiently. Responses to Conrad's presentation were positive, even garnering media attention by PC World.

Produced by analyst firm Coughlin and Associates, Storage Visions serves as a forum for industry leaders to discuss the issues impacting the storage industry.

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Please submit any future article ideas and topics to Conrad Maxwell, SATA-IO Marketing Chair, Silicon Image.

Sincerely,
SATA-IO Administration