17:
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One lesser-known feature of NCQ is that, unlike its ATA TCQ predecessor, it allows the host to specify whether it wants to be notified when the data reaches the disk's platters, or when it reaches the disk's buffer (on-board cache). Assuming a correct hardware implementation, this feature allows data
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while it is serving other (possibly new) requests under I/O pressure. Since the algorithms used inside drives' firmware for NCQ dispatch ordering are generally not publicly known, this introduces another level of uncertainty for hardware/firmware performance. Tests at Google around 2008 have shown
44:
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
158:
A 2004 test with the first-generation NCQ drive (Seagate 7200.7 NCQ) found that while NCQ increased IOMeter performance, desktop application performance decreased. One review in 2010 found improvements on the order of 9% (on average) with NCQ enabled in a series of
Windows multitasking tests.
84:
engine. NCQ's implementation is preferable because the drive has more accurate knowledge of its performance characteristics and is able to account for its rotational position. Both NCQ and TCQ have a maximum queue length of 32 outstanding commands. Because the ATA TCQ is rarely used,
250:(NVMe) standard also supports command queuing, in a form optimized for SSDs. NVMe allows multiple queues for a single controller and device, allowing at the same time much higher depths for each queue, which more closely matches how the underlying SSD hardware works.
144:
controller) even if AHCI is present on the host bus adapter, which makes initial setup more tedious and conversions of existing installations relatively difficult as most controllers cannot operate their ports in mixed AHCI–SATA/IDE/legacy mode.
92:
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.
179:
that NCQ can delay an I/O for up to 1–2 seconds. A proposed workaround is for the operating system to artificially starve the NCQ queue sooner in order to satisfy low-latency applications in a timely manner.
20:
NCQ allows the drive itself to determine the optimal order in which to retrieve outstanding requests. This may, as here, allow the drive to fulfill all requests in fewer rotations and thus less time.
243:
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.
120:
also natively support AHCI, but their AHCI support (via the msahci service) must be manually enabled via registry editing if controller support was not present during their initial install.
174:. There is no mechanism in NCQ for the host to specify any sort of deadlines for an I/O, like how many times a request can be ignored in favor of others. In theory, a queued request can be
69:
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 ATA TCQ.
679:
626:
321:""Re: DragonFly-2.3.1.165.g25822 master sys/dev/disk/ahci Makefile TODO ahci.c ahci.h ahci_attach.c ahci_cam.c ahci_dragonfly.c ahci_dragonfly.h atascsi.h""
282:
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parameters during its command sequence whereas TCQ interrupts the CPU during command queries and requires it to modulate the ATA host bus adapter's
240:'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.
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NCQ differs from TCQ in that, with NCQ, each command is of equal importance, but NCQ's host bus adapter also programs its own
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SSDs, the queue depth was even increased to support a maximum of 65,535 queues with up to 65,535 commands each.
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consistency to be guaranteed when the disk's on-board cache is used in conjunction with system calls like
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65:(TCQ). ATA's attempt at integrating TCQ was constrained by the requirement that ATA host bus adapters use
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profit significantly from being able to queue multiple commands for parallel workloads. For PCIe-based
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where the drive encounters latency on the host, rather than the other way around. For example,
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89:(and the IDE mode of some chipsets) usually only support one outstanding command per port.
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100:(AHCI), which allows operating systems to universally control them and enable NCQ.
608:"Intel's X25-E Extreme solid-state drive - Now with single-level cell flash memory"
105:
86:
58:
611:
247:
210:
187:
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http://www.seagate.com/docs/pdf/whitepaper/D2c_tech_paper_intc-stx_sata_ncq.pdf
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Yu, Y. J.; Shin, D. I.; Eom, H.; Yeom, H. Y. (2010). "NCQ vs. I/O scheduler".
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require the installation of a vendor-specific driver (similar to installing a
133:
37:
516:
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is disabled when NCQ is enabled, resulting in slower sequential performance.
431:
121:
117:
25:
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drives (with their supporting firmware). Older operating systems such as
305:"SATA II Native Command Queuing Overview", Intel Whitepaper, April 2003.
220:. The associated write flag, which is also borrowed from SCSI, is called
338:
633:
586:
374:"Seagate's Barracuda 7200.7 NCQ hard drive - The Tech Report - Page 13"
109:
491:
395:"Multitasking with Native Command Queuing - The Tech Report - Page 5"
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15:
627:"AHCI and NVMe as Interfaces for SATA Express Devices – Overview"
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166:, decreasing performance; this has been observed in practice on
141:
137:
456:"hard drive - Poor Linux software RAID 5 performance with NCQ"
129:
16:
339:"ahci(4) — Advanced Host Controller Interface for Serial ATA"
354:"ahci - Advanced Host Controller Interface for Serial ATA".
355:
517:"Disks from the Perspective of a File System - ACM Queue"
492:"Mark Lord: Re: Lower HD transfer rate with NCQ enabled?"
162:
NCQ can negatively interfere with the operating system's
294:Volume 1 of the final draft of the ATA-7 standard
680:Serial ATA and the 7 Deadly Sins of Parallel ATA
176:delayed by the drive an arbitrary amount of time
108:support AHCI natively since version 2.6.19, and
104:has supported AHCI with NCQ since 2.3 in 2009.
283:PDF white paper on NCQ from Intel and Seagate
8:
211:Disk buffer § Force Unit Access (FUA)
475:Gwendal Grignou, NCQ Emulation, FLS'08
413:
411:
275:
112:fully supports AHCI since version 8.0.
57:Native Command Queuing was preceded by
182:On some drives' firmware, such as the
124:'s AHCI enables not only NCQ but also
45:outstanding, most often occurring in
7:
606:Gasior, Geoff (November 23, 2008).
376:. The Tech Report. 17 December 2004
98:Advanced Host Controller Interface
14:
545:. Packt Publishing Ltd. p.
541:PostgreSQL 9.0: High Performance
397:. The Tech Report. 3 August 2005
96:Many newer chipsets support the
581:Jonathan Corbet (2010-08-18).
357:DragonFly On-Line Manual Pages
1:
625:Dave Landsman (2013-08-09).
583:"The end of block barriers"
420:ACM Transactions on Storage
725:
232:NCQ is also used in newer
208:
36:) is an extension of the
432:10.1145/1714454.1714456
654:"NVM Express Overview"
537:Gregory Smith (2010).
513:Marshall Kirk McKusick
76:engine with CPU-given
63:Tagged Command Queuing
30:Native Command Queuing
21:
477:talk summary (p. 109)
19:
49:-type applications.
343:BSD Cross Reference
494:. LKML. 2007-04-03
234:solid-state drives
228:Solid-state drives
195:solid-state drives
40:protocol allowing
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556:978-1-84951-031-8
222:Force Unit Access
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690:Hype vs. Reality
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82:third party DMA
74:first party DMA
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694:Tom's Hardware
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674:External links
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658:nvmexpress.org
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458:. Server Fault
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335:Matthew Dillon
326:
319:(2009-06-04).
317:Matthew Dillon
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260:I/O scheduling
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61:'s version of
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684:Lost Circuits
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347:DragonFly BSD
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265:Write barrier
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164:I/O scheduler
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114:Windows Vista
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106:Linux kernels
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102:DragonFly BSD
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692:analysis at
661:. Retrieved
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648:
637:. Retrieved
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590:. Retrieved
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521:. Retrieved
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496:. Retrieved
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460:. Retrieved
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399:. Retrieved
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378:. Retrieved
368:
356:
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329:
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245:
242:
231:
214:
205:Safety (FUA)
192:
186:circa 2007,
181:
161:
157:
95:
91:
87:Parallel ATA
71:
59:Parallel ATA
56:
33:
29:
23:
612:Tech Report
248:NVM Express
154:Performance
128:support on
709:Serial ATA
663:2014-11-26
639:2013-10-02
592:2015-06-27
523:2014-01-11
498:2014-01-11
462:2014-01-11
401:2014-01-11
380:2014-01-11
271:References
209:See also:
188:read-ahead
134:Windows XP
38:Serial ATA
686:(for TCQ)
184:WD Raptor
122:Windows 7
118:Windows 7
26:computing
703:Category
440:14414608
426:: 1–37.
337:(2009).
254:See also
634:SATA-IO
587:LWN.net
224:(FUA).
110:FreeBSD
53:History
553:
480:slides
438:
172:RAID-5
47:server
630:(PDF)
436:S2CID
238:Intel
218:fsync
193:SATA
170:with
168:Linux
551:ISBN
246:The
199:NVMe
142:SCSI
138:RAID
126:TRIM
116:and
682:at
428:doi
140:or
130:SSD
78:DMA
67:ISA
34:NCQ
24:In
705::
656:.
632:.
610:.
585:.
549:.
547:78
515:.
434:.
422:.
410:^
345:.
341:.
28:,
666:.
642:.
614:.
595:.
559:.
526:.
501:.
465:.
442:.
430::
424:6
404:.
383:.
360:.
349:.
323:.
32:(
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
