Introduction to IDE, SATA, SCSI, SAS, FC, SSD drive types [ZZ]

The main types of hard disk interfaces currently available are IDE, SATA, SCSI, SAS, FC, and so on. The IDE is commonly known as the port, SATA is commonly known as the serial port, both of the hard disk is the PC and low-end server common hard disk. SCSI is the abbreviation for "Small computer system dedicated interface", which is the hard disk with this interface. SAS is the SCSI interface of the serial port. The general server hard disk uses these two kinds of interface, its performance than the above two kinds of hard disk to be high, the stability is stronger, but the price is high, the capacity is small, the noise is big. FC is a fibre channel, and the Scis interface is the same as the fiber channel is not designed for the hard disk design and development of interface technology, is specifically designed for network systems, but with the demand for speed of the storage system, is gradually applied to the hard disk system. SSDs, also known as electronic hard disks or solid-state electronic disks, are hard disks made up of control units and solid-state storage units (DRAM or flash chips). SSD interface specification and definition, function and use of the same as the ordinary hard disk, in the product shape and size is also consistent with the ordinary hard disk. The new generation of SSDs generally uses the SATA-2 interface. But its cost is higher.

1. IDE

An abbreviation for the IDE (Integrated Drive Electronics Integrated driver Electronics), which is intended to refer to the hard drive that integrates the controller with the disk, is the transmission interface of a hard disk, and it has another name called ATA (Advanced technology Attachment), these two nouns all have the manufacturer to use, refers to the same thing.

The IDE's specifications later progressed, and the specification name of the Eide (enhanced IDE) was introduced, which is also known as Fast ATA. The difference is that fast ATA refers specifically to the hard drive interface, and Eide also has a standard for non-HDD products such as connecting discs. The IDE standard for connecting to non-hard disk classes is also known as the ATAPI interface. And then the faster interface, the name is only the ATA, such as Ultra Ata, ATA/66, ata/100 and so on.

Early IDE interfaces have two transmission modes, one is PIO (programming I/O) mode and the other is DMA (Direct Memory Access). Although the DMA mode system resource consumption is small, but requires additional drivers or settings, so the degree of acceptance is lower. Later, in the case of higher speed requirements, the DMA mode is more efficient, the operating system starts to support directly, and the manufacturer has introduced the increasingly fast standard of DMA mode transfer speed. Starting with Intel's 430TX chipset, it provides support for Ultra DMA 33, providing the maximum 33mb/sec data transfer rate, and then quickly evolving to ATA 66,ata 100 and Maxtor's ATA 133 standard, respectively, to provide 66mb/sec, Maximum data transfer rate for 100mb/sec and 133mb/sec. It is worth noting that Maxtor's ATA 133 standard does not have the industry's broad support, the hard disk manufacturers only maxtor themselves to use the ATA 133 standard, and Hitachi (IBM), Seagate and Western data are all ATA 100 standard, chipset manufacturers also only via,sis, Ali and Nviidia support the sub-standard, while Intel in chipset vendors only supports the ATA 100 standard.

The various IDE standards are well backwards compatible, such as ATA 133 compatible ATA 66/100 and Ultra DMA33, while the ATA 100 is also compatible with Ultra DMA 33/66.

It is important to note that for the ATA 66 and above IDE interface transmission standards, a dedicated 80-core IDE cable must be used, which adds 40 ground lines to improve signal stability compared to normal 40-core IDE cables.

2. SATA

A hard drive that uses SATA (Serial ATA) ports is called a serial drive. In 2001, the Serial ATA 1.0 specification was formally established by the Serial ATA Commission, which consists of Intel, APT, Dell, IBM, Seagate, Maxtor, and other major manufacturers.

The Serial ATA 2.0 specification (SATA II) was first established by the Serial ATA Board in 2002, although the associated equipment for serial ATA was not officially listed.

The Serial ATA uses a serial connection, the Serial ATA bus uses an embedded clock signal, has a stronger error correction capability, the biggest difference compared with the past is that the transmission instruction (not just the data) can be checked, if the error is automatically corrected, which greatly improves the reliability of data transmission. The serial interface also has the advantages of simple structure and hot-swappable support.

Serial drives are a new type of hard disk interface that is completely different from parallel ATA, known for transmitting data serially. Compared to parallel ATA, it has a lot of advantages.

a). Serial ATA transmits data serially and transmits only 1 bits of data at a time. This reduces the number of pins on the SATA interface, making the number of connected cables smaller and more efficient.

b). In fact, Serial ATA can do all the work with only four pins, respectively, for connecting cables, connecting ground wires, sending data and receiving data, and this architecture can also reduce system power consumption and reduce system complexity.

c). Serial ATA has a higher starting point and greater potential, and the Serial ATA 1.0 defines a data transfer rate of up to 150mb/s, which is higher than the fastest parallel ATA (that is, ata/133) that can achieve 133mb/s maximum data transfer rate, while in Serial ATA The data transfer rate of 2.0 reaches 300mb/s, and eventually SATA will achieve the highest data transfer rate of 600mb/s.

In the purchase of motherboards, there is no need to be too concerned about the IDE interface transmission standard how fast, in fact, the ATA 100,ata 133 and SATA 150 hard disk performance is similar, because limited by the mechanical structure of the hard disk and data access, hard disk performance bottleneck is the internal data transmission rate of the hard disk and not external interface standards , the current internal data transmission rate of the main drive is far from the 100mb/sec of ATA 100. So you have to follow your specific needs to buy.

3. SATA II

The speed of SATA is 1.5Gbps per second (150mb/sec), and the SATA2 (Serial ATA 2.0 specification) is 3Gbps (300mb/sec) per second. Sataⅱ interface motherboard can plug the SATA hard disk, SATA interface motherboard can not plug sataⅱ hard, this is backward compatible.

SATA II is developed on the basis of SATA, and its main feature is that the external transfer rate is further increased from 1.5G SATA to 3G, including NCQ (Native command Queuing, native commands queue), Port multiplexer (ports Multiplier), staggered start (staggered spin-up) and a series of technical features. Pure external transfer rate of 3Gbps is not true SATA II.

The key technology of SATA II is the external transfer rate and NCQ technology of 3Gbps. NCQ technology can optimize the order of command execution of the hard disk, avoid the same as the traditional hard disk in the order of receiving instructions to move the head read and write the different positions of the hard disk, in contrast, it will be ordered after receiving the command, the sorted head will be in a high-efficiency sequence to address, This avoids the loss caused by repetitive head movement and prolongs the life of the hard drive.

In addition, not all SATA hard drives can use NCQ technology, and the SATA controller of the motherboard chipset is required to support NCQ in addition to the hard disk itself to support NCQ. In addition, NCQ technology does not support the FAT file system, only the NTFS file system is supported.

As the SATA device market is chaotic, many SATA device providers abuse the "SATA II" in the marketing campaign, such as some of the "SATA II" hard drives are supported only 3Gbps and not support NCQ, and some only have 1.5Gbps hard disk but also support NCQ. As a result, Seagate (Seagate)-led Sata-io (Serial ATA International Organization,sata International, Original SATA workgroup) also announced the SATA 2.5 specification, which included the original SATA II has most of the features-from 3Gbps and NCQ to staggered start (staggered spin-up), hot-swappable (heat Plug), Port multiplexer (ports Multiplier), and newer eSATA (External SATA, External SATA interface) and so on.

It is important to note that some older motherboards that support only 1.5Gbps of South bridge chips (for example via VT8237 and Nvidia NForce2 MCP-R/MCP-GB) may not find a hard drive or a blue screen when using SATA II hard drives. However, most of the hard disk manufacturers have set a speed selection jumper on the hard disk to force the selection of 1.5Gbps or 3Gbps operating mode (few hard disk vendors are set by the corresponding tool software), as long as the hard disk is forced to set to 1.5gbps,sata II HDD can still be used on the old motherboard normally.

SATA hard drives are generally required to install the drivers provided by the motherboard chipset vendor when setting up RAID mode, but there are also a few older SATA RAID controllers that do not need to load drivers to build a raid in some versions of the Windows XP system with the latest patches.

4. SCSI

SCSI's English is all called "Small computer system Interface" (Small computer system interface), is a completely different interface with the IDE (ATA), the IDE interface is the standard interface of the ordinary PC, and SCSI is not specifically designed for the hard disk interface, is a kind of high-speed data transmission technology widely used in small-sized machines. The SCSI interface has a wide range of applications, multitasking, high bandwidth, low CPU usage, and hot plug, and so on, but the high price makes it difficult to use as IDE hard disk, so the SCSI hard disk is mainly used in medium and high-end servers and high-end workstations.

5. SAS

SAS (Serial attached SCSI) is a serial-attached SCSI and is a new generation of SCSI technology. The same as today's popular serial ATA (SATA) drives, serial technology is used to achieve higher transmission speeds and improve internal space by shortening the wiring. SAS is a new interface developed after the parallel SCSI interface. This interface is designed to improve the performance, availability, and scalability of storage systems and to provide compatibility with SATA drives.

SAS interface technology can be backwards compatible with SATA. In particular, the compatibility of the two is mainly embodied in the physical Layer and protocol layer compatibility.

a). In the physical layer, the SAS interface and the SATA interface are fully compatible, SATA hard drives can be used directly in the SAS environment, from the interface standard, SATA is a sub-standard SAS, so the SAS controller can directly control the SATA drive, However, SAS cannot be used directly in SATA environments because SATA controllers do not control SAS drives;

b). At the protocol level, SAS consists of 3 types of protocols, which are used to transmit data according to the different devices connected. Where the serial SCSI Protocol (SSP) is used to transport SCSI commands, SCSI Management Protocol (SMP) is used to maintain and manage connected devices, and SATA Channel Protocol (STP) is used for the transmission of data between SAS and SATA. So with these 3 protocols, SAS can be seamlessly combined with SATA and some SCSI devices.

The back panel (backplane) of the SAS system can connect both dual-port, high-performance SAS drives, and high-capacity, low-cost SATA drives. So SAS drives and SATA drives can exist in one storage system at the same time. However, it is important to note that the SATA system is not compatible with SAS, so SAS drives cannot be connected to the SATA backplane. Because of the compatibility of SAS systems, enabling users to use different interfaces of hard drives to meet the capacity or performance requirements of various applications, the expansion of the storage system with more flexibility, so that storage equipment to maximize the investment benefits.

In the system, each SAS port can connect up to 16,256 external devices, and SAS take direct point-to-time serial transmission, the transmission rate of up to 3Gbps, it is estimated that there will be 6Gbps or even 12Gbps of high-speed interface appears.

The SAS interface has also been significantly improved, providing both 3.5-inch and 2.5-inch interfaces, so it can be adapted to the needs of different server environments.

SAS relies on SAS extenders to connect more devices, the current Extender is mostly 12 ports, but according to the board manufacturer's product development plan, there will be 28, 36 port Extenders in the future to connect SAS devices, host devices or other SAS extenders.

Compared to the traditional parallel SCSI interface, SAS is not only significantly improved in interface speed (now the mainstream ultra-fast SCSI speed is 320mb/sec, and SAS is just starting at 300mb/sec, the future will reach 600mb/sec or even more), And because of the use of serial cables, not only can achieve a longer connection distance, but also improve the anti-jamming capability, and this thin cable can also significantly improve the heat dissipation inside the chassis.

The current shortcomings of SAS are mainly as follows:

a). There are few types of hard drives and control chips:

Only a handful of hard disk manufacturers, such as Seagate, Maxtor and Fujitsu, have introduced SAS interface drives, and many of the other vendors ' SAS hard drives are in the product's internal testing phase. In addition, the surrounding SAS controller chip or some SAS adapter cards are not many kinds, mostly concentrated in the hands of LSI and Adaptec Company.

b). The hard drive price is too expensive:

SAS drives are much more expensive than the same capacity ultra-SCSI drives. The high price has directly affected the user's purchase quantity and the Channel digest quantity, but cannot form the large-scale production SAS hard disk, its cost pressure will in turn causes the price to be unable to decline.

If users want to make a simple raid level, they need not only to buy multiple SAS hard drives, but also to purchase expensive RAID cards, which are essentially equivalent to the hard drive.

c). The actual transfer speed varies little:

SAS hard disk interface speed does not represent the speed of data transmission, limited by the mechanical structure of the hard disk, SAS hard disk is now almost the same mechanical structure and SCSI hard disk. At present, the bottleneck of data transmission is concentrated in the hard disk internal mechanical mechanism, hard disk storage technology, disk speed, determined by the internal drive data transmission speed, that is, about 80MBsec, SAS hard drive performance improvement is not obvious.

d). User pursuit of mature, stable products:

From the products now available, SAS hard disk is more used in high-end 4-way server, and more than 4 server users are not blindly pursuing high-speed hard disk interface technology, the most attractive to them should be mature, stable hardware products, although the SAS interface server and SCSI interface products in the speed, Stability is similar, but the current technology and products are not mature enough.

However, with Intel and other motherboard chipset manufacturers, Seagate and other hard disk manufacturers, as well as a large number of server manufacturers to promote the technology will gradually mature SAS, the price will gradually fall, sooner or later will become the main interface of the server hard disk.

6. FC

The English spelling of the Fibre Channel is fiber channel, and the Scis interface is the same as the fiber channel is not designed for the hard disk design and development of interface technology, is specifically designed for network systems, but with the demand for speed of the storage system, it is gradually applied to the hard disk system. Fibre Channel drives are developed to improve the speed and flexibility of a multi-drive storage system, which greatly improves the communication speed of multi-drive systems. The main features of Fibre Channel are hot-pluggable, high-speed bandwidth, remote connection, large number of connected devices and so on.

Fibre Channel is designed for multi-drive system environment such as server, which can meet the requirements of high-end workstations, servers, mass storage sub-networks, peripheral devices through hubs, switches and point-to-point connections, and so on.

7. SSD

SSD (solid state disk or solid State drive), also known as an electronic hard disk or an SSD, is a hard disk consisting of a control unit and a solid state storage unit (DRAM or Flash chip). SSD interface specification and definition, function and use of the same as the ordinary hard disk, in the product shape and size is also consistent with the ordinary hard disk. The solid-state drive has excellent seismic resistance because it does not have a rotating medium for ordinary hard drives. Its chip has a wide operating temperature range ( -40~85℃). Currently widely used in military, vehicle, industrial control, video surveillance, network monitoring, network terminals, power, medical, aviation, navigation equipment and other fields. At present, because of the high cost, is gradually popularized to the DIY market.

Because the SSD technology differs from the traditional hard disk technology, many new memory vendors are produced. Manufacturers can make solid-state drives by buying NAND memory and then matching the appropriate control chip. The new generation of SSDs generally uses the SATA-2 interface.

SSD storage medium is divided into two types, one is Flash (Flash chip) as a storage medium, the other is the use of DRAM as a storage medium.

(1) Flash-based Solid state drive (IDE flash disk, Serial ATA flash disk):

Flash chips are used as storage media, which is what we typically call SSDs. Its appearance can be made into a variety of shapes, such as: Notebook hard disk, micro hard disk, memory card, USB and other styles. The biggest advantage of this SSD is that it can be moved, and data protection is not controlled by power, can adapt to a variety of environments, but the service life is not high, suitable for the use of individual users.

In Flash-based SSDs, storage units are divided into two categories: SLC (single layer cell monolayer) and MLC (multi-level cell multilayer unit).

SLC is characterized by high cost, small capacity, but fast speed, and MLC is characterized by large capacity cost is low, but the speed is slow. Each MLC unit is 2bit, a whole lot more than the SLC. However, due to the large number of data stored in each MLC storage unit, the structure is relatively complex, the probability of error will increase and must be corrected, this action causes its performance significantly lag behind the structure of the simple SLC flash memory. In addition, the advantage of SLC flash memory is up to 100,000 times, 10 times times higher than MLC Flash. In addition, in order to ensure the life of MLC, control chip calibration and intelligent wear balancing technology algorithm, so that the number of writes per memory unit can be evenly distributed, up to 1 million hours of failure interval (MTBF).

(2) DRAM-based solid-state drives:

Using DRAM as storage medium, the application scope is narrow. It mimics the design of traditional hard drives, can be set up and managed by the filesystem tools of most operating systems, and provides an industry-standard PCI and FC interface for connecting to a host or server. The application method can be divided into SSD hard disk and SSD hard disk array two kinds. It is a high-performance memory, and the service life is very long, in the ointment is the need for independent power supply to protect data security.

Introduction to IDE, SATA, SCSI, SAS, FC, SSD drive types [ZZ]