Native Command Queuing (NCQ) is a technology designed to increase performance of SATA hard disks under certain conditions by allowing the individual hard disk to internally optimize the order in which received read and write commands are executed. This can reduce the amount of unnecessary drive head movement, 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.
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Native Command Queuing was preceded by Parallel ATA's version of Tagged Command Queuing (TCQ). ATA's attempt at integrating TCQ was constrained by the requirement that ATA host bus adapters use ISA bus device protocols to interact with the operating system. The resulting high CPU overhead and negligible performance gain contributed to a lack of market acceptance for TCQ.
NCQ differs from ATA TCQ in that in NCQ, the host bus adapter programmed its own first party DMA engine with the DMA parameters that the CPU gave when it issued the command, and that in ATA TCQ, the CPU must be interrupted by the ATA device so that the CPU can ask the ATA device which command is ready to be executed so that the CPU can program the ATA host bus adapter's third party DMA engine; and that each command is equal in importance in NCQ. This is preferable since the drive has the most knowledge of its performance characteristics, and is able to take rotational position into account. NCQ and PATA TCQ have a maximum queue length of 32 outstanding commands[1][2] (31 in practice).
For NCQ to be enabled, it must be supported and enabled in the SATA host bus adapter and in the hard drive itself. The appropriate driver must be loaded into the operating system to enable NCQ on the host bus adapter. Many newer chipsets support the Advanced Host Controller Interface (AHCI), which should allow a generic driver supplied by the operating system to control them and enable NCQ. In fact, newer mainstream Linux kernels support AHCI natively. Windows XP requires the installation of a vendor-specific driver even if AHCI is present on the host bus adapter. Windows Vista natively supports both AHCI and NCQ. FreeBSD fully supports AHCI and NCQ since version 8.0.
NCQ is also used in newer solid-state drives where the drive encounters latency on the host, rather than the other way around. For example, Intel's X25-E Extreme solid-state drive uses NCQ to ensure that the drive has commands to process while the host system is busy processing CPU tasks. [3]
Native Command Queuing (NCQ) is a technology designed to increase performance of SATA hard disks under certain conditions by allowing the individual hard disk to internally optimize the order in which received read and write commands are executed. This can reduce the amount of unnecessary drive head movement, 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.
Contents |
Native Command Queuing was preceded by Parallel ATA's version of Tagged Command Queuing (TCQ). ATA's attempt at integrating TCQ was constrained by the requirement that ATA host bus adapters use ISA bus device protocols to interact with the operating system. The resulting high CPU overhead and negligible performance gain contributed to a lack of market acceptance for TCQ.
NCQ differs from ATA TCQ in that in NCQ, the host bus adapter programmed its own first party DMA engine with the DMA parameters that the CPU gave when it issued the command, and that in ATA TCQ, the CPU must be interrupted by the ATA device so that the CPU can ask the ATA device which command is ready to be executed so that the CPU can program the ATA host bus adapter's third party DMA engine; and that each command is equal in importance in NCQ. This is preferable since the drive has the most knowledge of its performance characteristics, and is able to take rotational position into account. NCQ and PATA TCQ have a maximum queue length of 32 outstanding commands[1][2] (31 in practice).
For NCQ to be enabled, it must be supported and enabled in the SATA host bus adapter and in the hard drive itself. The appropriate driver must be loaded into the operating system to enable NCQ on the host bus adapter. Many newer chipsets support the Advanced Host Controller Interface (AHCI), which should allow a generic driver supplied by the operating system to control them and enable NCQ. In fact, newer mainstream Linux kernels support AHCI natively. Windows XP requires the installation of a vendor-specific driver even if AHCI is present on the host bus adapter. Windows Vista natively supports both AHCI and NCQ. FreeBSD fully supports AHCI and NCQ since version 8.0.
NCQ is also used in newer solid-state drives where the drive encounters latency on the host, rather than the other way around. For example, Intel's X25-E Extreme solid-state drive uses NCQ to ensure that the drive has commands to process while the host system is busy processing CPU tasks. [3]
NCQ also enables the SSD controller to complete commands concurrently (or partly concurrently, for example using pipelines) where the internal organisation of the device enables such processing.
For example, the SandForce 1200[4] based OCZ Vertex II 50GB drive running on a Dell Perc 5i (which doesn't support SATA NCQ) delivers about 7,000 4k IOPS (50% write) at a controller queue depth of 32 IOs. Moving the drive to the similar Dell Perc 6i increases this to over 14,000 IOPS on the same basis.
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Native Command Queuing (NCQ) is a technology designed to increase performance of SATA hard disks on computers. It can do this under certain situations by allowing the individual hard disk to internally optimize the order in which it executes the read and write requests it received. This can reduce the amount of unnecessary drive head movement and resulting in better performance (and slightly decreased wear of the drive) for workloads where multiple read/write requests are outstanding at the same time. This situation most often occurs in server-type applications. However, the current (as of 2004) technology actually slows down HD access in certain applications, like games and sequential reads and writes, because of the added latency induced by NCQ logic.[1][obsolete fact]
Native Command Queuing was preceded by Parallel ATA's version of Tagged Command Queuing (TCQ). ATA's attempt at integrating TCQ was constrained by the requirement that ATA host bus adapters use ISA bus device protocols to interact with the operating system. The resulting high CPU overhead and negligible performance gain contributed to a lack of market acceptance for TCQ.
NCQ differs from PATA TCQ in that the command re-ordering is performed by the drive rather than the operating system, and each command is equal in importance. This is preferable since the drive has the most knowledge of its performance characteristics, and is able to take rotational position into account. NCQ and PATA TCQ have a maximum queue length of 32 in-flight commands[2][3] (31 in practice[4]), while SCSI TCQ has a maximum queue length of 264 in-flight commands.
For NCQ to be enabled, it must be supported and enabled in the SATA host bus adapter and in the hard drive itself. The appropriate device driver must be loaded into the operating system to enable NCQ on the host bus adapter. Many newer chipsets support the Advanced Host Controller Interface (AHCI), which should allow a generic driver supplied by the operating system to control them and enable NCQ. In fact, newer mainstream Linux kernels support AHCI natively.[5] Unfortunately, Windows XP requires the installation of a vendor-specific driver even if AHCI is present on the host bus adapter. Windows Vista corrects this situation by including a generic AHCI driver.
  | Linux support status of various Serial ATA host bus adapters - Serial ATA (SATA) Linux hardware/driver status report |
| | Tom's Hardware Analysis of Hype vs. Reality - Can Command Queuing Turbo Charge SATA? : Can Command Queuing Turbo Charge SATA Hard Drives? - Review Tom's Hardware |
| | Explanation of what NCQ does - What is Native Command Queuing |
| | Test of Seagate Barracuda 7200.7 NCQ and other drives - Seagate's Barracuda 7200.7 NCQ hard drive - The Tech Report - Page 13 |
| | Serial ATA and the 7 Deadly Sins of Parallel ATA - Serial ATA and the 7 Deadly Sins of Parallel ATA - LostCircuits |
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