Serial ATA: hits & misses.It was a rising star in data storage. The technology promised new data speeds for desktop and laptop PCs, pencil-thin cables and power-thrifty electrical designs that would spawn a generation of smaller, cooler-running systems, and a price point that would drive down the cost of storage in enterprise environments. Designed as a replacement for ATA (1) (AT Attachment) The specification for IDE drives. See IDE. (2) See analog telephone adapter. ATA - Advanced Technology Attachment , the technology would be widely used in home and office PCs and stood to replace the venerable SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. in an increasing number of workstations and entry-level servers. Eventually, some pundits predicted, it would pack enough performance and reliability to displace SCSI as the mainstay for enterprise computing Refers to information technology in the larger company. See enterprise data and enterprise networking. . Today, nearly two years after the first Serial ATA See SATA. Serial ATA - Serial Advanced Technology Attachment products came to market, the technology is delivering on many of its promises, leaving others unfulfilled and raising high expectations for a generation of capabilities to come. [FIGURE 1 OMITTED] What Gave Rise to Serial ATA? Parallel ATA See PATA. has been the industry standard for connecting hard drives and other devices in desktop and mobile computers for more than a decade due to the technology's connection simplicity, low implementation costs and growing performance. But increasingly complex board designs, growing signal-timing requirements and other technological challenges are preventing parallel ATA from keeping pace with rising desktop performance demands. Enter Serial ATA, a technology designed chiefly for desktop systems as a replacement for ATA and to make smaller, faster computers possible. Serial ATA also was billed as a low-cost storage interconnect for workstations and entry-level servers that would deliver greater performance and reliability than ATA, ultimately offer connectivity for external storage and enable fan-out devices for greater scalability. Serial ATA also promised higher levels of scalability and reliability through serial signal transmissions, a method that, unlike parallel ATA technology, would deliver full bandwidth to each storage device. The technology would also eliminate the need for master/slave jumpers on ATA devices to simplify installation. When the Serial ATA blueprint was complete, the design called for a 10-year performance roadmap, compatibility with existing ATA software, a seamless transition path from ATA, and intent to target typical volume ATA applications. As a replacement for ATA, for example, Serial ATA would deliver more bandwidth to meet growing demand for higher performance gaming PCs. Serial ATA also added a hot-plug capability that would allow IT managers to expand storage on the fly and deepen ATA's penetration into the workstation and entry-level server markets. However, this optional feature has not been widely implemented, so end users must first ensure both the Serial ATA controller and disk drive support hot plug, and that the proper hot-plug cabling and backplane An interconnecting device that has sockets for printed circuit boards to plug into. Passive and Active Although resistors may be used, a "passive" backplane adds no processing in the circuit. are used to avoid potential disk drive damage. Serial ATA's Success, Desktop Replacement for ATA As a replacement for UDMA (Ultra DMA) See Ultra ATA. UDMA - ATA-4 disk drives in desktop systems, Serial ATA has been a resounding re·sound v. re·sound·ed, re·sound·ing, re·sounds v.intr. 1. To be filled with sound; reverberate: The schoolyard resounded with the laughter of children. 2. success. The initial promoters of the technology built strong and increasing industry support by maintaining a consistent and well-defined charter. The standards process was private, controlled by five companies, but well managed and open to broad industry participation. Today, Intel's south-bridges include two Serial ATA ports, and disk drives are available at multiple capacity and price points. Vendors are delivering on the promise of task file register software compatibility, bringing backward compatibility See backward compatible. (jargon) backward compatibility - Able to share data or commands with older versions of itself, or sometimes other older systems, particularly systems it intends to supplant. of Serial ATA controllers to existing ATA drivers already embedded in commercial operating systems Operating systems can be categorized by technology, ownership, licensing, working state, usage, and by many other characteristics. In practice, many of these groupings may overlap. . More desktop platforms are standardizing on Serial ATA as the primary disk storage interface and, at this juncture, a full transition from ATA to Serial ATA on the desktop is limited only by the availability of Serial ATA CD and DVD drives DVD drives come in a variety of speeds and options. The original drive (1x) transferred data at 1.35MB per second. By doubling the spindle speed (RPMs) for 2x drives, the transfer rate increased to 2.7MB/sec and has been increasing ever since. . Current CD-ROM CD-ROM: see compact disc. CD-ROM in full compact disc read-only memory Type of computer storage medium that is read optically (e.g., by a laser). and DVD DVD: see digital versatile disc. DVD in full digital video disc or digital versatile disc Type of optical disc. The DVD represents the second generation of compact-disc (CD) technology. drives--which use existing parallel ATA technology--remain in widespread use. The original Serial ATA specification was never meant to meet the needs of the high-end server and networked storage markets. To control development costs, Serial ATA 1.0 was developed without enterprise-class capabilities such as an advanced storage management protocol, scalable bandwidth for large numbers of drives, broad command queuing The ability to store multiple commands and execute them one at a time. , active dual-port capability, and support for simultaneous multi-initiator access required for clustered environments. Desktop Drives in Enterprise Environments As Serial ATA moved from laboratory to production in preparation for desktop deployments, a new class of data was rapidly growing: reference information. More small and mid-size businesses with modest IT budgets were digitizing information requiring bulk storage including e-mail, presentations, graphics and a variety of images including CAD/CAM CAD/CAM in full computer-aided design/computer-aided manufacturing. Integration of design and manufacturing into a system under direct control of digital computers. drawings, medical X-rays and bank checks, increasing demand for low-cost storage and forcing these businesses to seek a cost-effective alternative to high-end disk drives for storage of this infrequently accessed data. At the same time, many companies began to assign a value to information based on age, classifying data into two types: primary and secondary. Primary data, usually high-demand information used in applications such as credit card, bank and customer service databases and e-commerce, requires high-performance transactional disk drives that can withstand the rigors of round-the-clock access. As primary data ages, storage costs begin to outweigh performance, and businesses archive the data to lower cost disk drives in an Information Lifecycle Management Information Lifecycle Management refers to a wide-ranging set of strategies for administering storage systems on computing devices. Specifically, four categories of storage strategies may be considered under the auspices of ILM. (ILM) strategy that lends itself to using high-capacity Serial ATA desktop drives for bulk storage. Nearline storage Nearline storage (where Nearline is a contraction of Near-online) is a term used in computer science to describe an intermediate type of data storage. It is a compromise between online storage (constant, very rapid access to data) and offline storage (infrequent applications such as disk-to-disk back-up are another example of a workload where capacity is more important than performance. Serial ATA drives are ideal for both of these cost-sensitive environments since Serial ATA storage is optimized for capacity whereas enterprise-class disk drives such as SCSI are optimized for performance and reliability. Disk-to-disk backup is a growing practice as more businesses use the Internet to support round-the-clock operations and need to stage data for backup on disk drives before moving it to tape storage to maintain uninterrupted business operations Business operations are those activities involved in the running of a business for the purpose of producing value for the stakeholders. Compare business processes. The outcome of business operations is the harvesting of value from assets . Desktop drives, because they are designed for the light duty cycle associated with normal business hours BUSINESS HOURS. The time of the day during which business is transacted. In respect to the time of presentment and demand of bills and notes, business hours generally range through the whole day down to the hours of rest in the evening, except when the paper is payable it a bank or by a versus the 24X7 demands of enterprise storage, raise reliability concerns among IT managers wanting to deploy Serial ATA in the enterprise. High-port count Serial ATA RAID controllers have emerged to allay data availability Refers to the degree to which data can be instantly accessed. The term is mostly associated with service levels that are set up either by the internal IT organization or that may be guaranteed by a third party datacenter or storage provider. fears associated with deploying numerous desktop drives in these mission-critical storage environments. RAID technology provides uninterrupted data access in the event of a disk drive failure. A Look Ahead Even though the Serial ATA 1.0 specification was designed for the desktop, the cost savings of using Serial ATA disk drives in enterprise environments is so compelling that companies are willing to invest in additional technology to make Serial ATA suitable for use in the enterprise. The specification, for example, does not provide for LED control, though a blinking LED is critical in signaling drive failures in RAID environments. If an end user replaces the wrong Serial ATA drive, data is lost. With the completion of the Serial ATA 1.0 specification, the industry has turned to beefing up the protocol with enterprise enhancements. The goal is to provide a low-cost scalable interface that meets the infrastructure needs of high-performance transactional environments. Known as Serial ATA II Extensions, the updated specification defines features such as native command queuing, a 3-gigabit-per-second data transfer rate, basic enclosure services, staggered spin-up of disk drives, and new devices such as port multipliers to improve scalability and port selectors to improve reliability. Serial ATA II Extensions: A SCSI Replacement? Some Serial ATA proponents predict that SATA II See SATA. Extensions will ultimately replace the SCSI protocol, a highly unlikely outcome since SCSI's robustness for enterprise applications comes from 20 years of industry investment. That work has produced interfaces that deliver the highest levels of system reliability, scalability, performance and manageability. All the major enterprise interface technologies (including iSCSI, Fibre Channel, parallel SCSI Parallel SCSI (formally, SCSI Parallel Interface, or SPI) is one of the interface implementations in the SCSI family. In addition to being a data bus, SPI is a parallel electrical bus: There is one set of electrical connections stretching from one end of the SCSI bus and Serial Attached SCSI See SAS. ) use the proven SCSI protocol. Another barrier to Serial ATA's use in I/O-intensive transactional environments is total cost of ownership. While Serial ATA disk drives carry a much lower purchase price than enterprise-class drives, the ongoing hardware and management costs from frequently replacing failed drives not designed to withstand transactional workloads overshadows any initial cost advantage. Serial ATA disk drives, for example, lack the mechanical heft and sophistication so·phis·ti·cate v. so·phis·ti·cat·ed, so·phis·ti·cat·ing, so·phis·ti·cates v.tr. 1. To cause to become less natural, especially to make less naive and more worldly. 2. to support fast seek times, the random data patterns typical of transactional workloads, and the tolerance to rotational vibration caused when multiple drives in a single enclosure are seeking simultaneously. SCSI is undergoing the same transition as ATA, moving from a parallel to a serial architecture, namely Serial Attached SCSI. In doing so, Serial Attached SCSI will generate a larger potential base of customers for Serial ATA storage since the Serial Attached SCSI interface will support both Serial Attached SCSI and Serial ATA disk drives. Serial Attached SCSI will maintain backwards compatibility backwards compatibility - backward compatibility with existing Serial ATA connectors and cables, allowing IT managers to populate To plug in chips or components into a printed circuit board. A fully populated board is one that contains all the devices it can hold. a single dualmode controller or backplane with either drive type depending on the workload or application. Serial Attached SCSI is the follow-on technology to Ultra320 SCSI and will ultimately be the primary disk interface used in enterprise-class servers. Serial Attached SCSI also offers a performance roadmap extending from 3 gigabits/sec to 12 gigabits/sec, the unique ability to aggregate ports for scalable bandwidth and external cabling for connecting JBODs. The Serial Attached SCSI 1.0 specification was completed and ratified by INCITS INCITS INternational Committee for Information Technology Standards (InterNational Committee for Information Technology Standards The International Committee for Information Technology Standards, or INCITS (pronounced "insights" [1]), is an ANSI-accredited forum of IT developers. It was formerly known as the X3 and NCITS. ) in December 2003. At the same time, the Serial ATA II Extensions 1.1 specification is nearing completion pending final changes and clarifications. The first Serial Attached SCSI plugfest to demonstrate broad Serial Attached SCSI interoperability among early products was held in March. Serial Attached SCSI products will be available by the end of 2004. Conclusions/Predictions Serial ATA has reached a turning point. After launching in 2003, Serial ATA controllers are now shipping in volume, an increase driven largely by greater disk drive availability. Serial ATA is now on track to replace parallel ATA as the highest-volume disk drive interface. Serial ATA II devices, which are emerging to deliver 3-gigabit/sec performance, will spur further growth. Serial Attached SCSI is changing the way IT managers and systems builders are thinking about deploying disk drives in enterprise environments. For the first time, a single backplane will support the deployment of both enterprise and desktop disk drives. As a replacement for SCSI, Serial Attached SCSI disk drives will serve workloads where reliability and transaction processing Updating the appropriate database records as soon as a transaction (order, payment, etc.) is entered into the computer. It may also imply that confirmations are sent at the same time. Transaction processing systems are the backbone of an organization because they update constantly. are chief concerns. Optimized for cost-per-gigabyte, Serial ATA disk drives address the growing need for low-cost reference information storage. By supporting both disk drive types, Serial Attached SCSI backplanes will be the primary interconnect infrastructure for both reference and transactional data in enterprise environments. As a result, Serial ATA disk drives will find still a wider market once Serial Attached SCSI systems are available. In time, most Serial ATA disk drives in the enterprise will be connected to a Serial Attached SCSI infrastructure for two reasons: the Serial Attached SCSI interface offers unprecedented storage configuration flexibility and simplifies component design, testing, qualification, and inventory control while reducing related costs for system builders and IT managers.
Figure 2: Where Serial Attached SCSI and Serial ATA will play in servers
and desktops
Enterprise Environments
Desktop Reference Data Transactional Data
Environments
HDD Interface SATA SATA SAS
I/O Interface SATA SAS SAS
www.adaptec.com Linus Wong is director of Strategic Marketing and Paul Griffith is manager of Strategic Marketing, Storage Solutions Group, at Adaptec (Milpitas, CA) |
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