13-02-2010, 05:05 PM
[attachment=1984]
ABSTRACT
Serial ATA (SATA) is a computer bus technology primarily designed for transfer of data to and from a hard disk. SATA is a recent technological advancement of the standard IDE (ATA) hard drive interface. SATA employs a serial I/O communication bus instead of the parallel I/O bus used in ATA..
Serial ATA is a serial page link †a single cable with a minimum of four wires creates a point-to-point connection between devices. Transfer rates for SATA begin at 150 MBps.Compared with Parallel ATA, Serial ATA has lower signaling voltages and reduced pin count, is faster and more robust, and has a much smaller cable. Serial ATA is completely software compatible with Parallel ATA. Serial ATA technology allows for platform cost reductions and performance improvements while supporting a seamless transition from Parallel ATA technology. Configuration of Serial ATA storage devices is much simpler, with many of today's requirements for jumpers and settings no longer needed.
SATA II is the next set of SATA specifications after the initial SATA specification was written. SATA II specifications provide additional enhancements to SATA, delivered in increments.Features of SATA that increase performance levels include:Native Command Queuing (NCQ), RAID configurations with Serial ATA and Cyclic Redundancy Checking (CRC).Serial ATA will allow the performance of internal storage devices to continue to increase unabated for generations to come.
l.INTRODUCTION
In computer hardware, Serial ATA (Advanced Technology Attachment) is a computer bus technology primarily designed for transfer of data to and from a hard disk. It is the successor to the legacy AT Attachment standard (ATA).
Serial ATA (SATA) is an interface used to connect hard drives and other peripherals to a PC. It is the evolutionary replacement for the Parallel ATA (PATA) physical storage interface.
In other words, Serial ATA is a storage interface specification for the next-generation computing platform. This interface will be used to connect storage devices such as hard disc drives, DVDs, and CD-R/Ws to the motherboard and is the replacement for today's Parallel ATA physical storage interface.
Serial ATA technology allows for platform cost reductions and performance improvements while supporting a seamless transition from Parallel ATA technology. Serial ATA supplies storage interface headroom, beginning with 1.5 Gbps and scaling to 2x, 4x, and beyond. At the same time, Serial ATA is a drop-in solution that is compatible with existing ATA software drivers and runs on standard operating systems without modification. It provides for systems that are easier to design, with narrower cables that are simple to route and install, smaller cable connectors, improved silicon design, and lower voltages, which alleviate current design constraints in Parallel ATA. Configuration of Serial ATA storage devices is much simpler, with many of today's requirements for jumpers and settings no longer needed.
Serial ATA is 100% software compatible with today's ATA, but has a much lower pin count, enabling thinner, more flexible cables. Serial ATA's cables can be up to a meter in length, and are small and neat because they only need seven conductors or a seven-pin data connector. Serial ATA utilizes a point-to-point architecture and improved design that offers these performance enhancements:
Serial ATA is developed by Seagate as a founding member of the SATA-IO, replaces ATA and provides faster transfer of data with more flexibility in systems design.
SATA uses a 7 wire interface. Three of the wires are ground signals. The other 4 are two pairs of differential signals - one pair in each direction. SATA is using the transceiver technology used by Fiber (Fibre) Channel
Serial ATA can transport all ATA and ATAPI protocols, and is designed to be forward compatible with future ATA and SAT A standards.
Serial Cable
Serial ATA devices connect to systems using an inexpensive cable that provides compact connectors compatible with high-density server requirements.This allows Serial ATA to reduce the required number of signals from the 26 signals parallel ATA uses to 4.
Serial Transmission
Serial ATA uses 8B/10B serial transmission to transfer data over the serial cable.This high data-integrity scheme is widely accepted as the reigning de facto serial transmission scheme and is used in numerous technologies including Gigabit Ethernet and Fibre Channel.
Low Voltage Differential Signaling -Serial ATA uses low voltage differential signaling (LVD) consistent with low power and cooling requirements.
SATA 1.5 Gb/s
First-generation SATA interfaces, also known as SAT A/150, run at 1.5 gigabits per second. Serial ATA uses 8B/10B encoding at the physical layer. This encoding scheme has an efficiency of 80%, resulting in an actual data transfer rate of 1.2 gigabits per second, or 150 megabytes per second. The relative simplicity of a serial page link and the use of LVDS allow both the use of longer drive cables and an easier transition path to higher speeds.
SATA 3.0 Gb/s
Soon after SATA's introduction, enhancements were made to the standard. A 3Gb/s signalling rate was added to the physical layer, offering up to twice the data throughput. To ensure seamless backward compatibility between older SATA and the newer faster SATA 3Gb/s devices, the latter devices are required to support the original 1.5Gb/s rate. In practice, some older SATA systems that do not support SATA speed negotiation require the peripheral drive's speed be manually hardlimited to 150 MB/s with the use of a jumper for a 300 MB/s drive.
Like SATA 1.5Gb/s, SATA 3Gb/s uses 8B/10B encoding resulting in an actual data transfer rate of 2.4 Gb/s, or 300 MB/s.
The 3.0 Gb/s specification has been very widely referred to as Serial ATA II(SATA II), contrary to the wishes of the Serial ATA standards organization that authored it. The official website notes that SATA II was in fact that organization's name at the time, the SATA 3Gb/s specification being only one of many that the former SATA II defined, and suggests that SATA 3Gb/s be used instead.SATA 3Gb/s is sometimes also referred to as SATA 3.0, SATA II or SATA/300, continuing the line of PATA/100, PATA/133 and SATA/150.
The Serial ATA Working Group The Serial ATA Working Group is an industry organization whose mission is to define, develop, and deliver the industry specification for the Serial ATA interface. The Serial ATA Working Group is comprised of two groups:
¢ First, the Serial ATA 1.0 Working Group was established in February, 2000 to specify Serial ATA for desktop applications. Since that time, the organization has grown several-fold and now totals over 200 members.
¢ Second, the Serial ATA II Working Group was formed in February, 2002, to further address the needs of servers and networked storage market segments, and to specify next generation transfer speeds. The Serial ATA II Working Group is made up of over 86 members.
The SATA-IO is an independent, non-profit organization developed by leading industry companies to provide the industry with guidance and support for implementing the SATA specification as well as further developing the Serial ATA Interface. The SATA-IO promoters group includes Dell Computer Corporation, Intel Corporation, Maxtor Corporation, Seagate Technology and Vitesse Semiconductor.
2. NEED FOR SATA
Serial ATA was designed to overcome a number of limitations of Parallel ATA. Parallel ATA has been the hard disc drive interface for desktop PCs for over 15 years. The most significant limitation of Parallel ATA is the difficulty in increasing the data rate beyond 100 MBytes/s. Parallel ATA uses a single-ended signaling system that is prone to induced noise.
The Parallel ATA interface has a long history of design issues in spite of its success. Most of these issues have been successfully worked around, overcome, or simply ignored. They include:
¢ The 5-volt signaling requirement and high pin count (40-pin cable connectors)
¢ The 18-inch cable length limitation; cable width and cable routing problems
¢ Data robustness issues
5-Volt Signaling Requirement Since the industry continues to reduce chip core voltages, Parallel ATA's 5-volt signaling requirement is increasingly difficult to meet. Parallel ATA has 26 5-volt signals per ATA channel, requiring the use of large physical chip pads to accommodate the high pin count. The large pads will ultimately dominate the chip as chip sizes are reduced.
18-Inch Cable Length Limitation With the current Parallel ATA interface, the 18-inch cable length limitation can be a serious issue. The limited cable length complicates peripheral expansion choices, making some internal drive configurations impossible to implement. Of course, this depends on PC chassis size and the design and location of internal media bays.The wide, flat ribbon cables of the Parallel ATA bus are difficult to route, and their shape and bulk can restrict air flow and create hot spots inside the chassis. Data Robustness
With Parallel ATA, data robustness has been a long-standing issue. During its early development, no form of data checking was designed into the Parallel ATA interface. However, a degree of data protection was added in the form of CRC, which enabled the verification of interface data, for the first time when the first UDMA mode was introduced. Unfortunately, ATA command data is still not checked and remains a potential error source.
Increasing the Parallel data rate beyond 100 MBytes/s would require a new signaling system that would not be backward compatible with existing systems. As a result, a new interface system has been defined to accommodate the faster processing capabilities of next generation high-speed desktop, notebook and entry-server architectures.
Serial ATA has emerged as the industry standard internal storage interface designed to solve the bandwidth constraints of Parallel ATA, as well as well as the dependence on 5V signaling lines that are incompatible with silicon processes used in a wide variety of microprocessors. Serial ATA overcomes these issues by employing a 250mV differential signaling method. Differential signaling rejects induced noise. The 250mV differential signal level is compatible with future microelectronic fabrication processes.
Using serial technology with 8B /10B byte encoding completely bypasses the parallel transmission problems. 8B/10B encoding provides the essential embedded timing and significant data integrity checking provisions that high-speed transmission requires.Combined with 32-bit CRC checking at a data block level, the data integrity protection level far exceeds that of Parallel ATA and is comparable to higher-end disk interface technologies, including SCSI and Fibre Channel.
3. GENERAL OVERVIEW
Serial ATA is a high-speed serial page link replacement for the parallel ATA attachment of mass storage devices. The serial page link employed is a high-speed differential layer that utilizes Gigabit technology and 8b/10b encoding.
Figure 3.1 - Standard ATA device connectivity illustrates how two devices are connected to a standard ATA host adapter. This method allows up to two devices to be connected to a single port using a Master/Slave communication technique. Each device is connected via a ribbon cable that "daisy chains" the devices.
Operating system
Application I
ication 2
Standard ! ATA adapter
Application 3
DiskHiive DisOnve
Figure 3.1 - Standard ATA device connectivity
Figure 3.2 - Serial ATA connectivity illustrates how the same two devices are connected using a Serial ATA host adapter. In this diagram the dark grey portion is functionally identical to the dark grey portion of the previous diagram. Legacy host software that is only ATA aware accesses the Serial ATA subsystem in the exact same manner and will function correctly. In this case, however, the software views the two devices as if they were "masters" on two separate ports. The right hand portion of the host adapter is of a new design that converts the normal operations of the software into a serial data/control stream. The Serial ATA structure connects each of the two drives with their own respective cables in a point-to-point fashion.
Operating System
Application i
Serial ' ATA Adapter
Application 2
Application 3
Figure 3.2 - Serial ATA connectivity
4. BENEFITS OF SATA
Serial ATA offers a number of benefits over Parallel ATA, which includes the following: 1 .Serial ATA is faster
Serial ATA is faster than a parallel port. The COM port was never known for its speed. Today's most important standards (USB 2.0, Firewire, Ethernet, V-Link, MuTIOL, Hyper Transport, RapidIO) are all serial-based, yet they are fast and provide high performance. Serial ATA needs only two data channels †one for sending and one for receiving. These are supplied with a more modern 250 mV, in contrast to the 5 V typically used with IDE. With differential signaling, interference on one signal affects the other signal by the same amount. Because the signals run phase reversed, interference is self-canceling. Twisting the wires is no longer necessary. 2.Reduction in voltage
Serial ATA's low-voltage requirement (500 millivolts [mV] peak-to-peak) effectively alleviates the increasingly difficult-to-accommodate 5-volt signaling requirement. This requirement hampers the current Parallel ATA interface. 3.Cabling
The Serial ATA architecture replaces the wide Parallel ATA ribbon cable with a thin, flexible cable that can be up to 1 meter in length. The serial cable is smaller and easier to route inside the chassis. The small-diameter cable can help improve air flow inside the PC system chassis and facilitates future designs of smaller PC systems. The lower pin count of the smaller Serial ATA connector eliminates the need for the large and cumbersome 40-pin connectors required by Parallel ATA. 4.Improved Data Robustness
Serial ATA offers more thorough error checking and error correcting capabilities than was available with Parallel ATA. The end-to-end integrity of transferred commands and data can be guaranteed across the serial bus. Error rate is low as Serial ATA adds 32-bit CRC error correction for all bits transmitted. The 32-bit CRC used by Serial ATA can be shown to provide detection of two 10-bit errors up to a maximum frame size of 16384 bytes. This will provide for future expansion of Serial ATA FIS's to a maximum of 64 bytes of fixed overhead while still permitting a maximum user data payload of 8192 bytes
5 .Backward Compatibility
Serial ATA provides backward compatibility for legacy Parallel ATA and ATAPI devices. This can be accomplished by two methods. First, you can use chip sets that support Parallel ATA devices in conjunction with discrete components that support Serial ATA storage devices. These discrete components are now available. An integrated chip set, which supports a mix of serial and parallel channels, is also available. Second, you can use serial and parallel dongles, which adapt parallel devices to a serial controller or adapt serial devices to a parallel controller. 6.Increased Disc Drive Data Rates
Since disc drive data rates have not yet exceeded ATA 100 limits, why should you switch to Serial ATA? The maximum internal data rate on an IDE disc drive today is ~72MB/sec. The ATA/100 data transfer rate has not been reached. But one of the reasons IDE performance is where it is today is due to the expandable data path PATA has allowed.
7.Serial ATA Integration
The Serial ATA adoption will first take place with the introduction of Serial ATA drives and Host Bus Adapters in early 2003. By the second quarter of 2003, you will start to see Serial ATA motherboards integrated into desktop systems. One of the main objectives of the Serial ATA working group was that Serial ATA would not require any software changes. Serial ATA basically is 100% software compatible †meaning no changes are needed to current operating systems or applications. All you need is a Serial ATA drive, Serial ATA HBA, and Serial ATA interface cable and power adapter. 8.ATA Device Connectivity
By using a master/slave communication technique, Parallel ATA allows up to two devices to be connected to a single port. Both devices are daisy-chained together via one ribbon cable that is an unterminated multidrop bus. The standard parallel ATA software and device driver access the Serial ATA subsystem in exactly the same manner as parallel ATA and functions correctly. However, for Serial ATA the software views the two devices as if they were masters on two separate ports. The drive interface section of the host adapter uses a new design that converts the normal operations of the software into a serial data/control stream. The Serial ATA structure connects each of the two drives with individual cables in a point-to-point fashion.
Q.Bundled costs
Initially, Serial ATA is an added cost to the overall system since integrated motherboards are not always available. However, there are Serial ATA host bus adapter card solutions bundled or available from multiple vendors who are working with HDD vendors to derive compatible solutions. If SATA drives are significantly more costly to implement, it will be difficult to completely replace demand for parallel ATA,especially in the desktop market. SATA has been designed for cost equity with PATA drives. lO.Hot swap support.
Serial ATA supports hot-swapping via hardware support and by design of the connector. Hot swapping or hot plugging is the ability to remove and replace components of a machine, usually a computer, while it is operating. Once the appropriate software is installed on the computer, a user can plug and unplug the component without rebooting. A well-known example of this functionality is the Universal Serial Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard, or printer. It usually requires more sophisticated software and hardware than does plug-and-play.
In addition, the Serial ATA interface requires less voltage, meaning better power consumption and management in both desktop and mobile applications. The thinner cable allows for flexible designs and improved airflow in smaller form-factors. SATA allows disc drives to continue to offer performance and reliability at cost parity to Parallel ATA.
5.LAYERING MODEL
The Serial ATA function is divided into four layers, as shown in Table 1. The Transport and Link layers control overall operation. The Application layer is designed to appear identical to Parallel ATA, thereby maintaining software compatibility. The Physical layer handles the high speed serial communications between the host and device.
Serial ATA can transport all ATA and ATAPI protocols, and is designed to be forward compatible with future ATA and SATA standards.
4 Application
3 Transport
2 Link
1 Physical
Table : Serial ATA Communications Layer Model 5.1 Physical layer
The Serial ATA physical layer (PHY) uses low-voltage (250mV) differential signaling to enable speeds of 1.5Gb/s and beyond. The roadmap is designed to carry the interface for 10 years, through 6.0Gb/s. There are 2 differential pairs, one for transmit and one for receive. The PHY layer incorporates serializer/deserializer, provides out of band (OOB) signaling, and handles power-on sequencing and speed negotiation. Transmit Data is serialized from 10-bit characters, and Receive Data is deserialized to 10-bit characters. Device status feedback is provided to the to the page link layer.
5.1.1 List of services
¢ Transmit a 1.5 Gb/sec differential NRZ serial stream at specified voltage levels
¢ Provide a 100 Ohm matched termination (differential) at the transmitter
¢ Serialize a 10, 20, 40, or other width parallel input from the Link for transmission
¢ Receive a 1.5 Gb/sec +350/- 2650 ppm differential NRZ serial stream
¢ Provide a 100 Ohm matched termination (differential) at the receiver
¢ Extract data (and, optionally, clock) from the serial stream
¢ Deserialize the serial stream
¢ Detect the K28.5 comma character and provide a bit and word aligned 10, 20, 40, or other width parallel output
¢ Provide specified OOB signal detection and transmission
¢ Perform proper power-on sequencing and speed negotiation
¢ Provide device status to Link layer
¢ Optionally support power management modes
5.2 Link layer
The Link layer is responsible for sending and receiving frames, control signal primitives and performing flow control. The Link layer contains a primitive character encoder/decoder, 8B/10B encoder/decoder, 32-bit CRC calculator, data scrambler/descrambler and a layer controller.
5.2.1 Frame transmission
When requested by the Transport layer to transmit a frame, the Link layer provides the following services:
- Negotiates with its peer Link layer to transmit a frame, resolves arbitration conflicts if both host and device request transmission
- Inserts frame envelope around Transport layer data (i.e., SOF, CRC, EOF, etc.).
- Receives data in the form of Dwords from the Transport layer.
- Calculates CRC on Transport layer data.
- Transmits frame.
- Provides frame flow control in response to requests from the FIFO or the peer Link layer.
- Receives frame receipt acknowledge from peer Link layer.
- Reports good transmission or Link/Phy layer errors to Transport layer.
- Performs 8b/10b encoding
- Transforms (scrambles) control and data Dwords in such a way to distribute the potential EMI emissions over a broader range
5.2.2 Frame receipt
When data is received from the Phy layer, the Link layer provides the following services:
- Acknowledges to the peer Link layer readiness to receive a frame.
- Receives data in the form of encoded characters from the Phy layer.
- Decodes the encoded 8b/10b character stream into aligned Dwords of data.
- Removes the envelope around frames (i.e., SOF, CRC, EOF).
- Calculates CRC on the received Dwords.
- Provides frame flow control in response to requests from the FIFO or the peer Link layer.
- Compares the calculated CRC to the received CRC.
- Reports good reception or Link/Physical layer errors to Transport layer and the peer Link layer.
- Untransforms (descrambles) the control and data Dwords received from a peer Link layer.
5.2.3 Encoding method
Information to be transmitted over the Serial ATA bus shall be encoded a byte (eight bits) at a time along with a data or control character indicator into a 10-bit encoded character and then sent serially bit by bit. Information received over the Serial ATA bus shall be collected ten bits at a time, assembled into an encoded character, and decoded into the correct data characters and control characters. The 8b/10b code allows for the encoding of all 256 combinations of eight-bit data. A smaller subset of the control character set is utilized by Serial ATA.
The 8b/10b coding process is defined in two stages. The first stage encodes the first five bits of the unencoded input byte into a six bit sub-block using a
5B/6B encoder. The input to this stage includes the current running disparity value. The second stage uses a 3B/4B encoder to encode the remaining three bits of the data byte and the running disparity as modified by the 5B/6B encoder into a four bit value.
5.3 Transport layer
The Transport layer handles the packing and unpacking of ATA and AT API information into Frame Information Structures. The Transport layer also manages the FIFO or buffer memory for controlling data flow.
The Transport layer simply constructs Frame Information Structures (FIS's) for transmission and decomposes received Frame Information Structures. Host and device Transport layer state differ in that the source of the FIS content differs. The Transport layer maintains no context in terms of ATA commands or previous FIS content.
5.3.1 FIS construction
When requested to construct an FIS by a higher layer, the Transport layer provides the following services:
- Gathers FIS content based on the type of FIS requested.
- Places FIS content in the proper order.
- Manages Buffer/FIFO flow, notifies Link of required flow control.
- Receives frame receipt acknowledge from Link layer.
- Reports good transmission or errors to requesting higher layer.
5.3.2 FIS decomposition
When an FIS is received from the Link layer, the Transport layer provides the following services:
- Receives the FIS from the Link layer.
- Determines FIS type.
- Distributes the FIS content to the locations indicated by the FIS type.
- For the host Transport layer, receipt of an FIS may also cause the construction of an FIS to be returned to the device.
- Reports good reception or errors to higher layer
5.4 Application layer
The Application layer interacts with the Transport layer through a register interface that is equivalent to that presented by a traditional Parallel ATA host adapter. A shadow register block is defined that is both compatible with Parallel ATA and anticipated future extensions. Software is thus backward compatible with Parallel ATA devices. The Application layer is designed to appear identical to Parallel ATA, thereby maintaining software compatibility.
6.SATA DRIVE SPECIFICATION
¢ Capacity: 40GB, 60GB, 80GB, 100GB,120GB,160GB,240GB,300GB
¢ Rotational Speed: 5400 RPMJ200 RPM
¢ Interface: SATA II Extensions to Serial ATA 1.0a
¢ Native Command Queuing
¢ Hot Plug
¢ Best in Class Read / Write Power Consumption of 1.9W typ
¢ Idle Power Consumption of 0.6W typ
¢ Track to Track Seek Time: 1.5ms
¢ Host Transfer rate: 150 MB/s
7.CABLES AND CONNECTORS
The basic guidelines for Serial ATA connectors and cables are:
¢ Supporting 1.5 Gbps date rate with headroom for 3.0 Gbps speed
¢ Cost competitive to Ultra ATA connector and cable
¢ Facilitating smooth transition from Ultra ATA to Serial ATA
¢ Common connector interface for both 2.5" and 3.5" devices
From those guidelines, the following connector and cable objectives are derived:
¢ Minimal discontinuity at connectors
¢ Good impedance control for cable
¢ 0 to 1 meter cable length
¢ Low profile, fitting in the 2.5" drive
¢ Blind-mateable
¢ Hot-pluggable by means of staggered contacts
¢ Supporting power delivery with 12.0 V, 5.0 V, and 3.3 V voltages
Physically, the SATA power and data cables are the most noticeable change from Parallel ATA. The SATA standard defines a data cable using seven conductors and 8 mm wide wafer connectors on each end. SATA cables can be up to 1 m (39 in) long. PATA ribbon cables, in comparison, carry either 40- or 80-conductor wires and are limited to 46 cm (18 in) in length. The reduction in conductors makes SATA connectors and cables much narrower than those of PATA, thus making them more convenient to route within tight spaces and reducing obstructions to air cooling. Unlike early PATA connectors, SATA connectors are keyed ac" it is not possible to install cable connectors upside down without considerable force, and probably critically damaging one or both connectors.
The SATA standard also specifies a power connector sharply differing from the four-pin Molex connector used by PATA drives and many other computer components. Like the data cable, it is wafer-based, but its wider 15-pin shape should prevent confusion between the two. The power connector is known to be quite flimsy, as the thin plastic tops of the connectors (see power connector picture at right) will often break off when even the slightest force is used to wiggle it whilst it is plugged in (as is often required in tight spaces), rendering the connector useless. The seemingly large number of pins are
used to supply three different voltages if necessary ac" 3.3 V, 5 V, and 12 V. Each voltage is supplied by three pins ganged together (and 6 pins for ground). The supply pins are ganged together because the small pins by themselves cannot supply sufficient current for some devices. One pin from each of the three voltages is also used for hotplugging. The same physical connections are used on 3.5-in (90 mm) and 2.5-in (70 mm) (notebook) hard disks. Some SATA drives include a PATA-style 4-pin Molex connector for use with power supplies that lack the SATA power connector.
Adaptors are available to convert a 4-pin Molex connector to SATA power connector. However, because the 4-pin Molex connectors do not provide 3.3 V power, these adapters provide only 5 V and 12 V power and leave the 3.3 V lines disconnected. This precludes the use of such adapters with drives that require 3.3 V power. Understanding this, drive manufacturers have largely left the 3.3 V power lines unused.
8.DIFFERENCES BETWEEN PATA AND SATA
Parallel ATA Serial ATA
Up to 133 Mbytes/see Up to 150 Mbytes/sec (1.5 Gbits/see)
Tiny jumpers No master/slave, point to point
Eighteen-inch cable Up to 39-inch (1 -meter) cable
Two-inch-wide ribbon cable Thin cable (1/4-inch)
80 conductor 7-wire differential (noise canceling)
40 pin and socket Blade and beam connector (snap in)
Two-inch-wide data connector 1/2-inch-wide data connector
Onboard DMA controller First-party DMA support:
High 5V tolerance for legacy drives Low voltage (.25V) tolerance
Limited (legacy command queuing) Intelligent Data Handling
†Hot Swap
CRC on data only CRC on data, command, status
9.TECHNOLOGIES IN SATA
SATA makes it possible to design innovative, flexible and cost-effective storage solutions. The advanced features of SATA tend to fall into two main areas, increased performance and superior reliability.
Drive Performance in Demanding Workloads The high performance of SATA drives ensures that they will be able to scale to the needs of growing, complex computing environments. Features of SATA that increase performance levels include:
¢ Native Command Queuing (NCQ), taking place in the drive's firmware, can boost the performance of highly transactional applications as much as the performance of a 1 OK SATA drive.
¢ RAID configurations with Serial ATA, such as the easily configured RAID 0, can produce significant performance increases.
¢ Performance can scale to grow in areal density without saturating the interface bus for approximately ten years
Superior Reliability and Dependability SATA drives balance performance with increased reliability to ensure that data-intensive and critical applications can experience optimal uptime. SATA reliability features include the following:
¢ Cyclic Redundancy Checking (CRC) that integrates on both the command and the data packet level for enhanced bus reliability
¢ Newly designed cables and connectors that are more robust and increase overall system reliability
¢ Hot Plug for reducing system downtime if a storage failure should occur
¢ Native Command Queuing (NCQ) to reduce the mechanical workload on a native disc drive
9.1 NATIVE COMMAND QUEUING
Native Command Queuing (NCQ) is a technology designed to increase performance of SATA hard disks by allowing the individual hard disk to receive more than one I/O request at a time and decide which to complete first. Using detailed knowledge of its own seek times and rotational position, the drive can compute the best order to perform the operations. This can reduce the amount of unnecessary seeking (going back-and-forth) of the drive's heads, resulting in increased performance (and slightly decreased wear of the drive) for workloads where multiple simultaneous read/write requests are outstanding, most often occurring in server-type applications.
Native Command Queuing enables the hard drive to take multiple requests for data from the processor and re-arrange the order to maximize throughput.
Native Command Queuing is the second attempt to add Tagged Command queueing (TCQ) to the ATA hard drive system. First developed on SCSI drives, and widely used there, the original design of TCQ for PATA drives was very awkward and not widely implemented. The new name NCQ was coined for the completely new SATA design. There is no SCSI technology called NCQ because the existing SCSI TCQ is not seen as needing replacement.
Note that while command queuing can be a tremendous help if there are multiple outstanding I/O requests, NCQ adds a small amount of overhead to single requests, resulting in slightly lower performance on some single-threaded benchmarks typical of single-user computer use. The difference is never large.
For NCQ to be enabled, it must be supported and turned on in the SATA controller driver and in the hard drive itself. Method of activation varies depending on the controller. On some Intel chipset-based PC motherboards, this technology requires the enabling of the Advanced Host Controller Interface (AHCI) in the BIOS and the installation of the Intel Application Accelerator software on intel based systems.
NCQ is designed to improve performance and reliability as the transactional workload increases.When your application sends multiple commands to your drive, your drive can optimize the completion of these commands to reduce mechanical workload and improve performance.
¢ NCQ works in all systems supporting SATA NCQ from desktop PCs, workstations; digital media content servers, entry servers to high performance PCs and mobile/notebook systems
¢ Devices that support NCQ are 100% backward compatible with non-NCQ supporting systems
¢ NCQ allows the device to reorder commands for more efficient data transfers NCQ comprises three main components of functionality. Within each of them, Seagate includes capabilities that increase performance and durability of SATA drives.
¢ Command queue building in the drive: A SATA NCQ drive can either queue commands or execute them immediately. The drive knows what protocol to apply to different commands. It assigns a unique tag to commands.
¢ Transferring data for each command: NCQ lets the drive set up a direct memory access (DMA) operation for a data transfer without host software intervention. The drive controls the DMA engine, selects transfers to minimize latencies, and optimizes command ordering.
¢ Returning status for completed commands: The drive returns a status for completed commands. Command status is race-free, which means a status for any command can be communicated at any time, without a handshake between device and host. Host and drive use a 32-bit register to communicate about outstanding commands, and keep this register always accurate.
The results of NCQ are higher performance in heavy transactional workloads usually found in high performance workstations, network servers, multi¬media servers and editing workstations. But NCQ can also improve your overall system performance from booting your system to fde copying.
NCQ is designed into the Serial ATA interface but not all solutions have integrated it. To take advantage of Native Command Queuing it is necessary that both the host controller/chipset and hard drive support the feature
9.2 PORT MULTIPLIERS
Port multipliers are silicon-based devices that allow a single Serial ATA port to communicate with multiple drives.Port multipliers typically reside on an enclosure's backplane and are transparent to the drives. Port multipliers support all standard SATA drives.
Port Multiplier allows up to fifteen disks to be connected to the same port. While this number of disks will not likely be reached, Port Multipliers will likely attach between four to eight disks to one port. From a cost perspective, this is a very efficient solution.
Port multipliers allow cost-effective and expanded drive scalability to storage systems. Simplified cabling allows the host to be connected to up to fifteen SATA devices by a single cable.
A single host adapter occupying a single PCI slot is able to connect up to five times as many drives with no performance degradation on a 3Gb/s line.Until now Serial ATA (SATA) connectivity between drives and controllers has been an effective point-to-point relationship; a single drive connected to a single controller port via a single cable. The maximum number of drives in an array was predicated on the controller's port count.
The SATA Port Multiplier (SATA PM) specification permits a change to that point-to-point relationship with the introduction of port multiplication technology.Port multipliers allow easy, cost-effective storage expansion and push SATA's performance reach from sequential applications only to random applications as well. A port multiplier is a silicon-based unidirectional fan-out device, typically residing on an enclosure's backplane. It enables one host SATA PM enabled port to be connected to multiple SATA drives, similar to USB connectivity, but with the performance benefits of an aggregated switch. The port multiplier is transparent to the drives. The host knows that it is communicating to multiple drives, but the drives are unaware that they are
being multiplexed. The SATA drives function as if they were directly attached to the host adapter. Port multipliers support any standard SATA drive.
While it is possible to connect up to 15 drives to each SATA PM port via a port multiplier, drive connectivity is practically limited to the maximum available bandwidth on the 3 Gb/s link. Sustained I/O rates from the drives are kept to within the 3 Gb/s host port connection limit for maximum efficiency and performance.
Benefits of Port Multipliers
Port multipliers allow cost effective and expanded drive scalability to storage systems both inside and outside the box. Efficient add-on desktop storage with significantly higher performance than Firewire„¢ and USB 2.0 using external connections is assured. The number of extra drives that can be added to a conventional SATA system without port multipliers is limited to the controller's port count; additional drives mean additional controllers, effectively increasing the cost of the system. The user pays the cost of the extra controller(s) and necessarily forfeits additional PCI slots that may otherwise be needed for other peripheral upgrades. By using port multipliers, a single host adapter occupying a single PCI slot is able to connect four times as many drives with no performance degradation on a 3Gb/s line. SATA PM's simplified cabling topology where the host is connected to more drives by fewer cables is another plus for port multiplier connectivity. SATA's point-to-point relationship in which each port is connected to a single drive via a single cable means overly complicated cabling for multi-drive systems. A reduced cable count contributes to tidier backplanes, simpler drive insertion and removal, improved airflow inside the box, and a more secure system.
9.3 ADVANCED HOST CONTROLLER INTERFACE
The Advanced Host Controller Interface (AHCI) is a hardware mechanism that allows software to communicate with Serial ATA devices such as host bus adaptors. The specification details a system memory structure for computer hardware vendors, in order to transfer data between system memory and the device.The Advanced Host Controller Interface (AHCI) specification describes the register-level interface for a Host Controller for Serial ATA 1.0a and Serial ATA II. The specification includes a description of the hardware/software interface between system software and the host controller hardware. This specification is intended for hardware component designers, system builders, who help in system buiding and device driver (software) developers.
Implementation of the Advanced Host Controller Interface Specification requires a license from Intel. Contributors of the Advanced Host Controller Interface Specification for Serial ATA have signed the Advanced Host Controller Interface Specification for Serial ATA - Contributors Agreement in order to be licensed to use and implement this Specification. This Contributors Agreement provides Contributors with a reciprocal, royalty-free license to certain intellectual property rights from Intel and other Contributors for their products that are compliant with the licensed versions of the Advanced Host Controller Interface (AHCI) Specification for Serial ATA.
Intel intends to continue including suitable inputs, comments and suggestions from contributors to refine and update the Advanced Host Controller Interface Specification through a series of specification releases that will be marked as being Revision 1.x of the specification. Licensing of the applicable final specification of the AHCI Specification (As defined in the Contributors Agreement) allows the implementation of both discrete and integrated compliant AHCI host controllers. Licensing of the applicable draft version of the applicable specification level will allow the implementation of compliant, discrete Advanced host controllers (AHCI) only.
The latest revision of the specification is Revision 1.1. Subsequent Revision 1.x levels of the specification will be completed by Intel at its discretion as time and circumstances permit.
IQ.eSATA
Initially SATA was designed as an internal or inside-the-box interface technology, bringing improved performance and new features to internal PC or consumer storage. Creative designers quickly realized the innovative interface could reliably be expanded outside the PC, bringing the same performance and features to external storage needs instead of relying on USB or 1394 interfaces. Called external SATA or eSATA, customers can now utilize shielded cable lengths up to 2 meters outside the PC to take advantage of the benefits the SATA interface brings to storage. SATA is now out of the box as an external standard, with specifically defined cables, connectors, and signal requirements released as new standards in mid-2004. eSATA provides more performance than existing solutions and is hot pluggable. Key benefits of eSATA:
¢ Up to 6 times faster than existing external storage solutions: USB 2.0, & 1394
¢ Robust and user friendly external connection
¢ High performance, cost effective expansion storage
¢ Up to 2 meter shielded cables and connectors
¢ Full SATA speed for external disks (115 MB/s have been measured with external RAID enclosures)
¢ No protocol conversion from PATA/SATA to USB/Firewire, all disk features are available to the host
¢ Cable length is restricted to 2 metres, USB and Firewire span longer distances.
¢ Minimum and maximum transmit voltage decreased to 400 mV - 500 mV
¢ Minimum and maximum receive voltage decreased to 240 mV - 500 mV
Applications
External Direct Attached Storage for notebooks, desktop, consumer electronics and entry servers.
Many existing external hard drives use USB and/or 1394. These interfaces are not nearly as fast as SATA when compared using peak values, and can compromise drive performance.
The external cable connector is a shielded version of the connector specificed in SATA 1.0. The external connector and cable are designed for over five thousand insertions and removals while the internal connector is only specified to withstand fifty.
Currently, most PC motherboards do not have an e-SATA connector. eSATA is readily enabled, however, through the addition of an eSATA HBA or bracket connector (as shown above) for desktop systems or with a Cardbus or Express Card for notebooks. New motherboards introduced in 2005 will start to incorporate e-SATA connectors directly, making the addition of external storage an easy option.
The results of eSATA are dramatic and with no protocol overhead issues as with USB or 1394. The eSATA storage bus delivers as much as 37 times more performance. This ability is perfect for using an array of drives with performance striping behind the eSATA host port.
eSATA does not provide power, which means that external 2.5" disks which would otherwise be powered over the USB or Firewire cable need a separate power cable when connected over eSATA.
11.LIMITATIONS OF SATA
SATA have some limitations. SATA are designed to live alone in a PC, not in a server where it is coupled with many disks whose vibrations stress each other's bearings. Unexpected heat generation also becomes a serious factor due to multi-threaded activities.As for the protocol issue,there are at least three areas that taint.SATA's server potential:
¢ Performance
¢ Manageability
¢ Connectivity
Most of the performance limitations are due to mechanical issues. Furthermore, there is no value in a server application, where access profiles are largely random and command reordering gives top-notch benefits.
With SATA you only have one command to work with. For example, if you are using the disk for a video server, performance may be adequate.
When you purchase a RAID controller, it is because you want to preserve data integrity and functionality in the event of a disk failure. In the case of SATA, where the die-out rate of disks is higher, you especially want to use RAID. This is where the manageability limitation comes into the picture. Now that you have a failed disk drive, you want to replace it. With SATA, there is no indicator to show you which disk has failed. The user then runs the risk of losing invaluable data by pulling a functional disk instead of the failed disk.
Although SATA disks are inexpensive, the total SATA solution will not necessarily be low-cost. The main reason for this is because while using SATA 1.0 controllers, one can only connect one disk per port. If you need eight disk drives, you have to use eight ports.. Also, using SATA 1.0 controllers is not an efficient use of the transfer speed. Although SATA 1.0 touts a 150MB/sec peak speed, the fastest SATA disk drive is around 60MB/sec. In essence,each port is only using 60% to 70% of its potential.
12. SAT A II
SATA-II.which is an extension to the original SATA standard is seen as the bridging technology from a desktop-oriented SATA to a server-level storage interface, making it a viable, low-cost storage solution for server, NAS and SAN applications.
SATA II specifications provide additional enhancements to SATA, delivered in increments. The first increment, called "SATA II: Extensions to SATA 1.0" was released in 2H 2002 and focused on the immediate needs for the server and network storage segments.lt includes external connections,storage enclosures with multiple drives and port multipliers. Additional increments of the specification will focus on enhanced cabling, fan-out and failover capabilities and next generation signaling speeds. At IDF Spring 2003, two incremental developments were announced: a SATA II Port Multiplier specification release candidate and the completion and pending adoption of the SATA II Cables and Connectors Volume 1 specification.
There will always be a configuration and usage model that will require high end FC and SCSI drives, but SATA-II is making the server alternative viable,with all the economics and alternatives that go with it.
The introduction of Serial ATA II addresses the limitations of SATA 1.0 in order to make this interface a fit for large-scale professional deployment. There are five main features that epitomize Serial ATA II:
¢ Higher per-port transfer rate (3Gbs = 300MB/sec)
¢ Native Command Queuing
¢ Enclosure management
¢ Port multiplier
¢ Provides an upgrade path to SAS
It may sound strange to increase the per-port transfer rate.With one disk connected to one port, 150MB/sec is a waste of bandwidth because one disk cannot possibly utilize all that bandwidth.However, because SATA II will allow users to connect multiple disks to the same port.
Native Command Queuing enables the hard drive to take multiple requests for data from the processor and re-arrange the order to maximize throughput.
Enclosure management is the solution to identify the failed disk, in the case of a SATA RAID user. The same protocols used for SCSI and Fibre Channel monitoring will be ported to SATA, completely bridging the gap on this front.
The 3.0 Gb/s specification has been very widely referred to as "Serial ATA II" ("SATA II"), contrary to the wishes of the Serial ATA standards organization that authored it. A 3Gb/s signalling rate offers up to twice the data throughput. To ensure seamless backward compatibility between older SATA and the newer faster SATA 3Gb/s devices, the latter devices are required to support the original 1.5Gb/s rate. The official website notes that SATA II was in fact that organization's name at the time, the SATA 3Gb/s specification being only one of many that the former SATA II defined, and suggests that "SATA 3Gb/s" be used instead. SATA II has grown in popularity as the name for the SATA 3 Gb/s data transfer rate, causing great confusion with customers .SATA II is not the brand name for SATA's 3Gb/s data transfer rate, but the name of the organization formed to author the SATA specifications. The group has since changed names, to the Serial ATA International Organization, or SATA-IO.
13. CONCLUSION
Serial ATA is planned as the foundation of a new storage interface replacement architecture that is as cost-effective as Parallel ATA and has greater performance improvement potential.
SATA technology provides a new serial interconnect designed to change the way vendors develop storage systems. The first deployments, where cost is an important issue, are intended for entry-level servers and network-attached storage. As the infrastructure continues to develop, SATA will play in low-end servers and more complex storage systems.
Serial ATA will enable future client system performance increases that are required to keep pace with other system enhancements. The transition will also ease implementation, power consumption, and design issues for computer systems companies.
Serial ATA technology provides a consistent platform for the ongoing development and deployment of directattached and networked storage applications offering enhanced performance and reliability. Serial ATA overcomes the limitations of parallel ATA by providing an improved point-to-point signaling configuration, reduced pin count, lower voltage, smaller connectors, and thinner cabling. Going forward, storage vendors from across the globe will provide a wide range of SATA products for use in multiple market segments. Serial ATA introduces a roadmap that provides the industry with scalable performance for the next 10 years.
14. FUTURE SCOPE
The most compelling reason to move to SATA is that the specification roadmap will support historical trends for performance for another 10 years. Phase II of the Serial ATA specification will improve the I/O of each drive to 3.0 gigabits per second (300 MB/s). Parallel ATA will likely be frozen at 133 MB/s and most manufacturers only support 100 MB/s.
SATA-IO plans to make a 6.0 Gb/s standard. Although the theoretical throughput would be doubled, conventional hard disks cannot approach saturating this speed. The 6.0 Gb/s standard will however be useful in combination with port multipliers, which allow multiple drives to be connected to one Serial ATA port, as well as with solid-state drives such as RAM disk.
15. BIBLIOGRAPHY
1. serialata.org
2. en.wikipediawiki/Serial_ATA
3. webopedia.eom/TERM/S/Serial_ATA.html
4. seagateproducts/interface/sata
5. lsilogictechnologies/industry_standards/sata ata technology.html
wwwl .hpproducts/servers/proliantstorage/serial/sata/index.html
CONTENTS
Page Number
1. INTRODUCTION 1
2. NEED FOR SATA 4
3. GENERAL OVERVIEW 6
4. BENEFITS OF SATA 8
5. LAYERING MODEL 11 5.1) PHYSICAL LAYER 11 5.2 )LINK LAYER 12 5.3)TRANSPORT LAYER 14 5.4)APPLICATION LAYER 15
6.SATA DRIVE SPECIFICATION 16
7.CABLES AND CONNECTORS 17
8. DIFFERENCES BETWEEN PATA AND SATA 19
9.TECHNOLOGIES IN SATA 20
9.1 )NATIVE COMMAND QUEUING 21
9.2)PORT MULTIPLIERS 23
9.3)ADVANCED HOST CONTROLLER INTERFACE 25
lO.eSATA 26
11 .LIMITATIONS OF SATA 28
12.SATA II 29
13.CONCLUSION 31
14.FUTURE SCOPE 32
15.BIBLIOGRAPHY 33
