Editing Native Command Queuing (section)

=== Safety (FUA) ===
{{See also|Disk buffer#Force Unit Access (FUA)}}

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 consistency to be guaranteed when the disk's on-board cache is used in conjunction with system calls like [[fsync]].<ref>{{cite web|author=Marshall Kirk McKusick|author-link=Marshall Kirk McKusick|url=http://queue.acm.org/detail.cfm?id=2367378 |title=Disks from the Perspective of a File System - ACM Queue |publisher=Queue.acm.org |access-date=2014-01-11}}</ref> The associated write flag, which is also borrowed from SCSI, is called [[Force Unit Access]] (FUA).<ref name="Smith2010">{{cite book|author=Gregory Smith|title=PostgreSQL 9.0: High Performance|url=https://archive.org/details/postgresqlhighpe00smit|url-access=limited|year=2010|publisher=Packt Publishing Ltd|isbn=978-1-84951-031-8|page=[https://archive.org/details/postgresqlhighpe00smit/page/n98 78]}}</ref><ref>{{Cite web| title=Native Command Queuing | url=http://www.seagate.com/docs/pdf/whitepaper/D2c_tech_paper_intc-stx_sata_ncq.pdf | archive-url=https://web.archive.org/web/20040517234919/http://www.seagate.com:80/docs/pdf/whitepaper/D2c_tech_paper_intc-stx_sata_ncq.pdf | archive-date=2004-05-17}}</ref><ref>{{cite web
 | url = https://lwn.net/Articles/400541/
 | title = The end of block barriers
 | date = 2010-08-18 | access-date = 2015-06-27
 | author = Jonathan Corbet | publisher = [[LWN.net]]
}}</ref>