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USB Attached SCSI – Wikipedia

USB Connected SCSI (UAS) or USB Connected SCSI Protocol (UASP) is a pc protocol used to maneuver knowledge to and from USB storage units resembling exhausting drives (HDDs), solid-state drives (SSDs), and thumb drives. UAS is determined by the USB protocol, and makes use of the usual SCSI command set. Use of UAS typically offers sooner transfers in comparison with the older USB Mass Storage Bulk-Solely Transport (BOT) drivers.

UAS was launched as a part of the USB 3.zero customary, however may also be used with units complying with the slower USB 2.zero customary, assuming use of suitable {hardware}, firmware and drivers.


UAS is outlined throughout two requirements, the T10 “USB Connected SCSI” (T10/2095-D) known as the “UAS” specification, and the USB “Common Serial Bus Mass Storage Class – USB Connected SCSI Protocol (UASP)” specification. The T10 technical committee of the Worldwide Committee for Info Know-how Requirements (INCITS) develops and maintains the united statesspecification; the SCSI Commerce Affiliation (SCSITA) promotes the united statestechnology. The USB mass-storage gadget class (MSC) Working Group develops and maintains the united states specification; the USB Implementers Discussion board, Inc. (USB-IF) promotes the united states expertise.

UAS drivers typically present sooner transfers when in comparison with the older USB Mass Storage Bulk-Solely Transport (BOT) protocol drivers.[1][2][3] Though UAS was added within the USB 3.zero customary, it may also be used at USB 2.zero speeds, assuming suitable {hardware}.[4]

When used with an SSD, UAS is significantly sooner than BOT for random reads and writes, however nonetheless properly beneath the pace of a local SATA Three interface (6 Gbit/s).[5]

Many NVMe to USB adapters are the USB Connected SCSI units.[6]

{Hardware} assist[edit]

A quick {hardware} roundup in July 2010 by SemiAccurate discovered that Gigabyte Know-how had launched working UAS drivers for his or her boards utilizing NEC/Renesas chips, and that—on the {hardware} stage at the very least—”the LucidPort USB 300 and USB302, Symwave SW6315, Texas Devices TUSB9260 and the VLI VL700 controllers all assist UASP, whereas so far as we may discover, the ASMedia ASM1051 and ASM1051E in addition to the Fujitsu MB86C30A doesn’t.”[1]

A comparative efficiency overview by VR-Zone in August 2011, concluded that solely the NEC/Renesas chips had UAS working drivers.[7] The identical Renesas UAS driver (for Home windows) additionally works with AMD’s A70M and A75 Fusion Controller Hubs,[8] the USB a part of which was co-developed by AMD and Renesas.[9] In October 2011, ASMedia chips had gained driver assist as properly (that they had assist on the {hardware} aspect earlier than).[10] Fujitsu lists some higher-end chips just like the MB86C311A that do assist UAS.[11]

As for assist by Intel Platform Controller Hub (PCH), an article in MyCE notes: “The native Intel USB3 UASP answer is simply supported below Home windows 8. To additional complicate issues, not all Z77 motherboards assist USB3 UASP. A license is required to implement UASP, and never all motherboard producers are ready to go on the additional value of this license to the tip consumer.”[12]

Working system assist[edit]

Microsoft added native assist for UAS to Home windows 8.[13] Drives supporting UAS load Uaspstor.sys as an alternative of the older Usbstor.sys.[14] Home windows Eight helps UAS by default over USB 2.zero as properly.[15] UAS drivers and merchandise are licensed by Microsoft utilizing the Home windows {Hardware} Certification Equipment.[16]

Apple added native assist for UAS to OS X 10.Eight Mountain Lion; drives utilizing UAS present up in (Apple menu -> About This Mac) -> System Info -> Software program -> Extensions as IOUSBAttachedSCSI (or IOUSBMassStorageUASDriver, relying on the model of OS X) “Loaded: Sure”.[17] Drives listed with “Loaded: No” are defaulting to the older, slower Bulk Solely Transport (BOT) mode. This will happen if the drive’s USB controller, the Mac’s USB port, or any connected USB hub would not assist UASP mode.

The Linux kernel has supported UAS since Eight June 2014 when the model 3.15 was launched.[18]
Nevertheless, some distributions of Linux resembling Ubuntu (from v11.xx onwards) have suffered from points with the implementation of the united statesprotocol. In some non-UAS supported USB HDD drives, the drive isn’t mountable by the working system. A reported workaround is to blacklist the united statesmodule in modprobe.[19]

FreeBSD doesn’t assist UAS as of August 2018.[20]

  • Designed to immediately handle the failings of the USB mass-storage gadget class bulk-only transports (BOT)
    • Permits command queuing and out-of-order completions for USB mass-storage units
    • Eliminates software program overhead for SCSI command phases
    • Permits TRIM (UNMAP in SCSI terminology) operation for SSDs [21]
  • As much as 64Ok instructions could also be queued
  • SCSI SAM-Four compliant
  • USB 3.zero SuperSpeed and USB 2.zero Excessive-Velocity variations outlined
    • USB 3.zero SuperSpeed – host controller (xHCI) {hardware} assist, no software program overhead for out-of-order instructions
    • USB 2.zero Excessive-speed – Considerably allows command queuing in USB 2.zero drives
  • Streams have been added to the USB 3.zero SuperSpeed protocol for supporting UAS out-of-order completions
    • USB Three host controller (xHCI) offers {hardware} assist for streams

See additionally[edit]


Exterior hyperlinks[edit]

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