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SCSI Command
In SCSI computer storage, computers and storage devices use a client-server model of communication. The computer is a client which requests the storage device to perform a service, e.g., to read or write data. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with Fibre Channel, iSCSI, Serial Attached SCSI, and other transport layers. In the SCSI protocol, the initiator An initiator can refer to: * A person who instigates something. * Modulated neutron initiator, a neutron source used in some nuclear weapons ** Initiator, an Explosive booster ** Initiator, the first Nuclear chain reaction * Pyrotechnic initiato ... sends a SCSI command information unit to the target device. Data information units may then be transferred between the computer and device. Finally, the device sends a response information unit to the computer. SCSI commands are sent in a command descriptor block (CDB), which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI
Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interfaces. The SCSI standard defines command sets for specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements. The initial Parallel SCSI was most commonly used for hard disk drives and tape drives, but it can connect a wide range of other devices, including scanners and CD drives, although not all controllers can handle all devices. The ancestral SCSI standard, X3.131-1986, generally referred to as SCSI-1, was published by the X3T9 technical committee of the American National Standards Institute (ANSI) in 1986. SCSI-2 was published in August 1990 as X3.T9.2/86-109 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Storage
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but less expensive and larger options further away. Generally, the fast volatile technologies (which lose data when off power) are referred to as "memory", while slower persistent technologies are referred to as "storage". Even the first computer designs, Charles Babbage's Analytical Engine and Percy Ludgate's Analytical Machine, clearly distinguished between processing and memory (Babbage stored numbers as rotations of gears, while Ludgate stored numbers as displacements of rods in shuttles). This distinction was extended in the Von Neumann a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parallel SCSI
Parallel SCSI (formally, SCSI Parallel Interface, or SPI) is the earliest of the interface implementations in the SCSI family. SPI is a parallel bus; there is one set of electrical connections stretching from one end of the SCSI bus to the other. A SCSI device attaches to the bus but does not interrupt it. Both ends of the bus must be terminated. SCSI is a peer-to-peer peripheral interface. Every device attaches to the SCSI bus in a similar manner. Depending on the version, up to 8 or 16 devices can be attached to a single bus. There can be multiple hosts and multiple peripheral devices but there should be at least one host. The SCSI protocol defines communication from host to host, host to a peripheral device, and peripheral device to a peripheral device. The Symbios Logic 53C810 chip is an example of a PCI host interface that can act as a SCSI target. SCSI-1 and SCSI-2 have the option of parity bit error checking. Starting with SCSI-U160 (part of SCSI-3) all commands and d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fibre Channel
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data centers. Fibre Channel networks form a switched fabric because the switches in a network operate in unison as one big switch. Fibre Channel typically runs on optical fiber cables within and between data centers, but can also run on copper cabling. Supported data rates include 1, 2, 4, 8, 16, 32, 64, and 128 gigabit per second resulting from improvements in successive technology generations. The industry now notates this as Gigabit Fibre Channel (GFC). There are various upper-level protocols for Fibre Channel, including two for block storage. Fibre Channel Protocol (FCP) is a protocol that transports SCSI commands over Fibre Channel networks. FICON is a protocol that transports ESCON commands, used by IBM mainframe computers, over Fibre Ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ISCSI
Internet Small Computer Systems Interface or iSCSI ( ) is an Internet Protocol-based storage networking standard for linking data storage facilities. iSCSI provides block-level access to storage devices by carrying SCSI commands over a TCP/IP network. iSCSI facilitates data transfers over intranets and to manage storage over long distances. It can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval. The protocol allows clients (called ''initiators'') to send SCSI commands ( ''CDBs'') to storage devices (''targets'') on remote servers. It is a storage area network (SAN) protocol, allowing organizations to consolidate storage into storage arrays while providing clients (such as database and web servers) with the illusion of locally attached SCSI disks. It mainly competes with Fibre Channel, but unlike traditional Fibre Channel which usually requires dedicated cabling, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI Initiator
In computer data storage, a SCSI initiator is the endpoint that initiates a SCSI session, that is, sends a SCSI command. The initiator usually does not provide any Logical Unit Numbers (LUNs). On the other hand, a SCSI target is the endpoint that does ''not'' initiate sessions, but instead waits for initiators' commands and provides required input/output data transfers. The target usually provides to the initiators one or more LUNs, because otherwise no read or write command would be possible. Detailed information Typically, a computer is an initiator and a data storage device is a target. As in a client–server architecture, an initiator is analogous to the client, and a target is analogous to the server. Each SCSI address (each identifier on a SCSI bus) displays behavior of initiator, target, or (rarely) both at the same time. There is nothing in the SCSI protocol that prevents an initiator from acting as a target or vice versa. SCSI initiators are sometimes wrongly called ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI Target
In computer data storage, a SCSI initiator is the endpoint that initiates a SCSI session, that is, sends a SCSI command. The initiator usually does not provide any Logical Unit Numbers (LUNs). On the other hand, a SCSI target is the endpoint that does ''not'' initiate sessions, but instead waits for initiators' commands and provides required input/output data transfers. The target usually provides to the initiators one or more LUNs, because otherwise no read or write command would be possible. Detailed information Typically, a computer is an initiator and a data storage device is a target. As in a client–server architecture, an initiator is analogous to the client, and a target is analogous to the server. Each SCSI address (each identifier on a SCSI bus) displays behavior of initiator, target, or (rarely) both at the same time. There is nothing in the SCSI protocol that prevents an initiator from acting as a target or vice versa. SCSI initiators are sometimes wrongly calle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI CDB
In SCSI standards for transferring data between computers and peripheral devices, often computer storage, commands are sent in a Command Descriptor Block (CDB). Each CDB can be a total of 6, 10, 12, or 16 bytes, but later versions of the SCSI standard also allow for variable-length CDBs. The CDB consists of a one byte operation code followed by some command-specific parameters. The parameters need not be a full byte long, and the parameter length varies from one command to another. The available commands, with links to articles describing the detailed structure of many of them, are listed in the article section List of SCSI commands. Typical CDB structures, for the 6- and 16-byte SCSI Request Sense Command Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ..., opcode 3, are: 6-byte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SCSI Status Code
A SCSI Status Code is used to determine the success or failure of a SCSI command. At the end of any command, the target returns a Status Code byte which should be one of the following: 00h Good This status code indicates that the device has completed the task successfully. 02h Check Condition When the target returns a Check Condition in response to a command it is indicating that it has entered a contingent allegiance condition. This means that an error occurred when it attempted to execute a SCSI command. The initiator usually then issues a SCSI Request Sense command in order to obtain a Key Code Qualifier ( KCQ) from the target. 04h Condition Met This status code is returned on successful completion of a Pre-fetch Command. 08h Busy The target returns Busy if it cannot complete a command at that time, for example if it is in the contingent allegiance condition. 10h Intermediate (obsolete) The target returns Intermediate when it successfully completes a linked command (ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trim (computing)
A trim command (known as TRIM in the ATA command set, and UNMAP in the SCSI command set) allows an operating system to inform a solid-state drive (SSD) which blocks of data are no longer considered to be 'in use' and therefore can be erased internally. Trim was introduced soon after SSDs were introduced. Because low-level operation of SSDs differs significantly from hard drives, the typical way in which operating systems handle operations like deletes and formats resulted in unanticipated progressive performance degradation of write operations on SSDs. Trimming enables the SSD to more efficiently handle garbage collection, which would otherwise slow future write operations to the involved blocks.Shimpi, Anand Lal. (18 March 2009). p. 10. TRIM is an ATA command (Advanced Technology Attachment Command) that allows an OS to inform SSD about the blocks of data no longer in use. The SSD then deletes such blocks of data to make a way for newer blocks of data. TRIM is basically used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seagate Technology
Seagate Technology Holdings plc is an American data storage company. It was incorporated in 1978 as Shugart Technology and commenced business in 1979. Since 2010, the company has been incorporated in Dublin, Ireland, with operational headquarters in Fremont, California, United States. Seagate developed the first 5.25-inch hard disk drive (HDD), the 5-megabyte ST-506, in 1980. They were a major supplier in the microcomputer market during the 1980s, especially after the introduction of the IBM XT in 1983. Much of their growth has come through their acquisition of competitors. In 1989, Seagate acquired Control Data Corporation's Imprimis division, the makers of CDC's HDD products. Seagate acquired Conner Peripherals in 1996, Maxtor in 2006, and Samsung's HDD business in 2011. Today, Seagate, along with its competitor Western Digital, dominates the HDD market. History Founding as Shugart Technology Seagate Technology (then called Shugart Technology) was incorporated on No ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
