Editing Serial Attached SCSI

{{short description|Point-to-point serial protocol for enterprise storage}}
{{More citations needed|date=November 2012}}
{{Infobox computer hardware bus
| name        = SAS
| fullname    = Serial Attached SCSI
| image       = SFF-8484-internal-connector-0a.jpg
| alt         = Four red cables lead into a wide black electrical connector
| caption     = SAS connector
| invent-date = 
| invent-name = 
| super-name  = 
| super-date  = 
| replaces    = 
| width       = 1
| numdev      = 65,535
| speed       = {{unbulleted list|SAS-1: Full-duplex<ref>{{Cite web|title=Differences between SAS and SATA|url=https://kb.sandisk.com/app/answers/detail/a_id/10510/~/differences-between-sas-and-sata}}</ref> 3&nbsp;Gbit/s (2004)|SAS-2: Full-duplex 6&nbsp;Gbit/s (2009)|SAS-3: Full-duplex 12&nbsp;Gbit/s (2013)|SAS-4: Full-duplex 22.5&nbsp;Gbit/s (2017)<ref name="24G-scsita">{{cite web | title = 24G SAS Data Storage Specification Development Complete; SCSI Trade Association Spotlights Technology at 2017 Flash Memory Summit | url = http://www.scsita.org/content/library/24g-sas-data-storage-specification-development-complete-scsi-trade-association-spotlights-technology-at-2017-flash-memory-summit/ | date = 2017-08-07 | publisher = SCSI Trade Association }}</ref>}}
| style       = s
| hotplug     = Yes
| external    = 
}}

In [[computing]], '''Serial Attached SCSI''' ('''SAS''') is a point-to-point serial [[Communications protocol|protocol]] that moves data to and from [[Computer storage|computer-storage]] devices such as [[hard disk drive]]s, [[solid-state drive]]s and [[tape drive]]s. SAS replaces the older [[Parallel SCSI]] (Parallel Small Computer System Interface, usually pronounced "scuzzy" <ref name="ThompsonThompson2003">{{cite book |first1=Robert Bruce |last1=Thompson |first2=Barbara Fritchman |last2=Thompson|title=PC Hardware in a Nutshell: A Desktop Quick Reference|url=https://books.google.com/books?id=kG8LcWfruOAC&pg=PT308|date=24 July 2003|publisher="O'Reilly Media, Inc."|isbn=978-0-596-55234-3|page=422}}</ref><ref name="NCR1990">{{cite book|author=NCR Corporation|title=Scsi: understanding the small computer system interface|url=https://archive.org/details/scsiunderstandin00ncrc|url-access=registration|year=1990|publisher=Prentice Hall|location=University of Virginia|language=English|page=[https://archive.org/details/scsiunderstandin00ncrc/page/5 5]|isbn=9780137968558 }}</ref>) bus technology that first appeared in the mid-1980s. SAS, like its predecessor, uses the standard [[SCSI command|SCSI command set]]. SAS offers optional compatibility with [[Serial ATA]] (SATA), versions 2 and later. This allows the connection of SATA drives to most SAS [[backplane]]s or controllers. The reverse, connecting SAS drives to SATA backplanes, is not possible.<ref>
{{cite web 
| url = https://storage.microsemi.com/en-us/_whitepapers/tech/sata/sas_sata_unprlcompat.htm 
| title = SAS and SATA: Unparalleled Compatibility | access-date = 2024-05-20
}}
</ref>

The T10 technical committee of the [[International Committee for Information Technology Standards]] (INCITS) develops and maintains the SAS protocol; the [[SCSI Trade Association]] (SCSITA) promotes the technology.

==Introduction==
[[File:HuaweiRH2288HV2.JPG|thumb|upright=1.7|Storage servers housing 24 SAS hard disk drives per server]]

A typical Serial Attached SCSI system consists of the following basic components:

# An ''initiator'': a device that originates device-service and [[Task Management Function|task-management]] requests for processing by a target device and receives responses for the same requests from other target devices. Initiators may be provided as an on-board component on the motherboard (as is the case with many server-oriented motherboards) or as an add-on [[host bus adapter]].
# A ''target'': a device containing logical units and target ports that receives device service and task management requests for processing and sends responses for the same requests to initiator devices. A target device could be a hard disk drive or a [[disk array]] system.
# A ''service delivery subsystem'': the part of an [[input/output|I/O]] system that transmits information between an initiator and a target. Typically cables connecting an initiator and target with or without expanders and backplanes constitute a service delivery subsystem.
# ''Expanders'': devices that form part of a service delivery subsystem and facilitate communication between SAS devices. Expanders facilitate the connection of multiple SAS End devices to a single initiator port.<ref>{{cite web|title=SAS architecture|url=https://www-01.ibm.com/support/knowledgecenter/POWER6/arebj/sasoverview.htm#|publisher=ibm|access-date=January 14, 2016}}</ref>

==History==
* SAS-1: 3.0&nbsp;Gbit/s, introduced in 2004<ref name="roadmap">{{cite web|url=http://www.scsita.org/library/2015/10/serial-attached-scsi-technology-roadmap.html|title=Serial Attached SCSI Master Roadmap|publisher=SCSI Trade Association|date=2015-10-14 |access-date=2016-02-26}}</ref>
* SAS-2: 6.0&nbsp;Gbit/s, available since February 2009
* SAS-3: 12.0&nbsp;Gbit/s, available since March 2013
* SAS-4: 22.5&nbsp;Gbit/s called "24G",<ref name="SAS4">{{Cite web|url=http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas4r06.pdf |title=Serial Attached SCSI - 4 (SAS-4) draft |publisher=T10 |date=2016-05-11 |access-date=2016-05-15}}</ref> standard completed in 2017<ref name="roadmap" /><ref name="24G-scsita" />
* SAS-5: 45&nbsp;Gbit/s development started 2018<ref name="sas-5r1a">{{cite web |title=Serial Attached SCSI - 5 (SAS-5) |url=http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas5r01a.pdf |website=t10.org |publisher=T10/BSR INCITS 561 |access-date=2024-01-17 |date=2019-02-22}}</ref>

==Identification and addressing==
A ''SAS Domain'' is the SAS version of a SCSI domain&mdash;it consists of a set of SAS devices that communicate with one another by means of a service delivery subsystem. Each SAS port in a SAS domain has a SCSI port identifier that identifies the port uniquely within the SAS domain, the [[World Wide Name]]. It is assigned by the device manufacturer, like an [[Ethernet]] device's [[MAC address]], and is typically worldwide unique as well. SAS devices use these port identifiers to address communications to each other.

In addition, every SAS device has a SCSI device name, which identifies the SAS device uniquely in the world. One does not often see these device names because the port identifiers tend to identify the device sufficiently.

For comparison, in parallel SCSI, the SCSI ID is the port identifier and device name. In [[Fibre Channel]], the port identifier is a WWPN and the device name is a WWNN.

In SAS, both SCSI port identifiers and SCSI device names take the form of a ''SAS address'', which is a 64 bit value, normally in the NAA IEEE Registered format. People sometimes refer to a SCSI port identifier as ''the'' SAS address of a device, out of confusion. People sometimes call a SAS address a World Wide Name or WWN, because it is essentially the same thing as a WWN in Fibre Channel. For a SAS expander device, the SCSI port identifier and SCSI device name are the same SAS address.

== {{Anchor|DUAL-DOMAIN}}Comparison with parallel SCSI ==
{{More citations needed section|date=May 2014}}

* The SAS "bus" operates [[Point-to-point (network topology)|point-to-point]] while the SCSI bus is [[Multidrop bus|multidrop]]. Each SAS device is connected by a dedicated link to the initiator, unless an expander is used. If one initiator is connected to one target, there is no opportunity for [[Bus contention|contention]]; with parallel SCSI, even this situation could cause contention.
* SAS has no [[Electrical termination|termination]] issues and does not require terminator packs like parallel SCSI.
* SAS eliminates [[clock skew]].
* SAS allows up to 65,535 devices through the use of expanders, while Parallel SCSI has a limit of 8 or 16 devices on a single channel.
* SAS allows a higher transfer speed (SAS-1, SAS-2, SAS-3, and SAS-4 supports data bandwidth of 3, 6, 12, and 24&nbsp;Gbits/sec, respectively)<ref>[https://www.techtarget.com/searchstorage/definition/serial-attached-SCSI#:~:text=Serial%2DAttached%20SCSI%20standards%20are,%2D4%2C%20supports%2024%20&nbsp;Gbps. DEFINITION : Serial-Attached SCSI (SAS)]</ref> than most parallel SCSI standards. SAS achieves these speeds on each initiator-target connection, hence getting higher throughput, whereas parallel SCSI shares the speed across the entire multidrop bus.
* SAS devices feature dual ports, allowing for redundant backplanes or [[multipath I/O]]; this feature is usually referred to as the ''dual-domain SAS''.<ref>{{cite web
 | url = http://h20565.www2.hpe.com/hpsc/doc/public/display.html?docId=emr_na-c01451157
 | archive-url = https://web.archive.org/web/20160110234427/http://h20565.www2.hpe.com/hpsc/doc/public/display?docId=emr_na-c01451157
 | title = Redundancy in enterprise storage networks using dual-domain SAS configurations
 | date = May 2008 | access-date = 2016-01-10 | archive-date = 2016-01-10
 | publisher = Hewlett-Packard Development Company | format = PDF
}}</ref>
* SAS controllers may connect to SATA devices, either directly connected using native SATA protocol or through SAS expanders using Serial ATA Tunneling Protocol (STP).
* Both SAS and parallel SCSI use the [[SCSI]] command set.

== {{Anchor|VS-SATA}}Comparison with SATA ==
There is little physical difference between SAS and SATA.<ref name="steadfast">{{cite web |url = http://old.steadfast.net/services/hdd.dedicated.hosting.php |title = SATA vs SAS Hard Drives on Dedicated Servers |access-date = 2013-08-05 |website=Steadfast.net |publisher=Steadfast |archive-url=https://web.archive.org/web/20130629051809/http://old.steadfast.net/services/hdd.dedicated.hosting.php |archive-date=29 June 2013 |url-status=dead}}</ref>

* SAS protocol provides for multiple initiators in a SAS domain, while SATA has no analogous provision.<ref name="steadfast" />
* Most SAS drives provide [[tagged command queuing]], while most newer SATA drives provide [[native command queuing]].<ref name="steadfast" />
* SATA uses a command set that is based on the [[parallel ATA]] command set and then extended beyond that set to include features like native command queuing, hot-plugging, and TRIM. SAS uses the SCSI command set, which includes a wider range of features like error recovery, reservations and block reclamation. Basic ATA has commands only for direct-access storage. However SCSI commands may be tunneled through [[Parallel ATA#ATAPI|ATAPI]]<ref name="steadfast" /> for devices such as [[CD-ROM|CD]]/DVD drives.
* SAS hardware allows [[multipath I/O]] to devices while SATA (prior to [[SATA&nbsp;2.0]]) does not.<ref name="steadfast" /> Per specification, SATA&nbsp;2.0 makes use of port multipliers to achieve port expansion, and some port multiplier manufacturers have implemented multipath I/O using port multiplier hardware.
* SATA is marketed as a general-purpose successor to parallel ATA and {{As of|2009|alt=has become}} common in the consumer market, whereas the more-expensive{{When? |reason=claim requires source|date=January 2024}} SAS targets critical server applications.
* SAS error-recovery and error-reporting uses SCSI commands, which have more functionality than the ATA [[Self-Monitoring, Analysis and Reporting Technology|SMART]] commands used by SATA drives.<ref name="steadfast" />
* SAS uses higher signaling voltages (800–1,600&nbsp;mV for transmit, and 275–1,600&nbsp;mV for receive{{Clarify|date=May 2015}}) than SATA (400–600&nbsp;mV for transmit, and 325–600&nbsp;mV for receive{{Clarify|date=May 2015}}). The higher voltage offers (among other features) the ability to use SAS in server backplanes.<ref name="steadfast" />
* Because of its higher signaling voltages, SAS can use cables up to {{convert|10|m|ft|abbr=on}} long, whereas SATA has a cable-length limit of {{convert|1|m|ft|abbr=on|sigfig=2}} or {{convert|2|m|ft|abbr=on|sigfig=2}} for [[eSATA]].<ref name="steadfast" />
* SAS is [[full duplex]], whereas SATA is [[half duplex]]. The SAS transport layer can transmit data at the full speed of the link in both directions at once, so a SCSI command executing over the link can transfer data to and from the device simultaneously. However, because SCSI commands that can do that are rare, and a SAS link must be dedicated to an individual command at a time, this is generally not an advantage with a single device.<ref>{{cite web |first1=Patrick |last1=Schmid |first2=Achim |last2=Roos |url=http://www.tomshardware.com/reviews/sas-6gb-hdd,2392-2.html |title=SAS Features And Basics - Next-Generation SAS: 6 Gb/s Storage Hits The Enterprise |publisher=Tom's Hardware |date=2009-08-31 |access-date=2014-07-15}}</ref>

==Characteristics==

===Technical details===
The Serial Attached SCSI standard defines several [[OSI layers|layers]] (in order from highest to lowest): application, transport, port, link, PHY and physical. Serial Attached SCSI comprises three transport protocols:

* Serial SCSI Protocol (SSP){{snd}} for command-level communication with SCSI devices.
* Serial ATA Tunneling Protocol (STP){{snd}} for command-level communication with SATA devices.
* Serial Management Protocol (SMP){{snd}} for managing the SAS fabric.

For the Link and [[PHY]] layers, SAS defines its own unique protocol.

At the [[physical layer]], the SAS standard defines connectors and voltage levels. The physical characteristics of the SAS wiring and signaling are compatible with and have loosely tracked that of SATA up to the 6&nbsp;Gbit/s rate, although SAS defines more rigorous physical signaling specifications as well as a wider allowable differential voltage swing intended to allow longer cabling. While SAS-1.0 and SAS-1.1 adopted the physical signaling characteristics of SATA at the 3&nbsp;Gbit/s rate with [[8b/10b encoding]], SAS-2.0 development of a 6&nbsp;Gbit/s physical rate led the development of an equivalent SATA speed. In 2013, 12&nbsp;Gbit/s followed in the SAS-3 specification.<ref>{{cite web | url = http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas3r06.pdf | title = Serial Attached SCSI - 3 (SAS-3) | access-date = 2015-05-11 | date = 2013-11-07 | publisher = T10}}</ref> SAS-4 is slated to introduce 22.5&nbsp;Gbit/s signaling with a more efficient 128b/150b encoding scheme to realize a usable data rate of 2,400&nbsp;MB/s while retaining compatibility with 6 and 12&nbsp;Gbit/s.<ref>{{cite web|url=http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas4r01.pdf |title=Serial Attached SCSI - 4 (SAS-4), 5.8.1 General electrical characteristics |access-date=2015-05-11}}</ref>

Additionally, [[SCSI Express]] takes advantage of the [[PCI Express]] infrastructure to directly connect SCSI devices over a more universal interface.<ref>{{cite web | url = http://www.scsita.org/library/scsi-express/ | title = Library » SCSI Express | access-date = 2013-08-05 | publisher = SCSI Trade Association}}</ref>

===Architecture===
[[File:The architecture of SAS layers.svg|thumb|upright=1.9|The architecture of SAS layers]]

SAS architecture consists of six layers:
* Physical layer:
** defines electrical and physical characteristics
** differential signaling transmission
** Multiple connector types:
*** [[Small Form Factor committee|SFF]]-8482 – [[Serial ATA|SATA]] compatible
*** Internal four-lane connectors: SFF-8484, SFF-8087, SFF-8643
*** External four-lane connectors: SFF-8470, SFF-8088, SFF-8644
* PHY Layer:
** [[8b/10b encoding|8b/10b data encoding]] (3, 6, and 12&nbsp;Gbit/s)
** 128b/150b SPL packet encoding (22.5&nbsp;Gbit/s)<ref name="SPL4">{{Cite web|url=http://www.t10.org/cgi-bin/ac.pl?t=f&f=spl4r08a.pdf |title=SAS Protocol Layer - 4 (SPL-4) draft, p. |publisher=T10 |date=2016-05-09 |access-date=2016-05-15}}</ref> (2&nbsp;bit header, 128&nbsp;bit payload, 20&nbsp;bit [[Reed–Solomon error correction|Reed-Solomon]] [[forward error correction]])
** Link initialization, speed negotiation and reset sequences
** Link capabilities negotiation (SAS-2 onwards)
* Link layer:
** Insertion and deletion of primitives for clock-speed disparity matching
** Primitive encoding
** [[scrambler|Data scrambling]] for reduced [[Electromagnetic interference|EMI]]
** Establish and tear down native connections between SAS targets and initiators
** Establish and tear down tunneled connections between SAS initiators and SATA targets connected to SAS expanders
** Power management (proposed for SAS-2.1)
* Port layer:
** Combining multiple PHYs with the same addresses into wide ports
* Transport layer:
** Contains three transport protocols:
*** Serial SCSI Protocol (SSP): for command-level communication with SCSI devices
*** Serial ATA Tunneled Protocol (STP): for command-level communication with SATA devices
*** Serial Management Protocol (SMP): for managing the SAS fabric
* Application layer

===Topology===
An [[SCSI initiator|initiator]] may connect directly  to a [[SCSI target|target]] via one or more [[PHY]]s (such a connection is called a port whether it uses one or more PHYs, although the term ''wide port'' is sometimes used for a multi-PHY connection).

===SAS expanders===
The components known as ''Serial Attached SCSI Expanders'' (SAS Expanders) facilitate communication between large numbers of SAS devices. Expanders contain two or more external expander-ports. Each expander device contains at least one SAS Management Protocol target port for management and may contain SAS devices itself. For example, an expander may include a Serial SCSI Protocol target port for access to a peripheral device. An expander is ''not necessary'' to interface a SAS initiator and target but allows a single initiator to communicate with more SAS/SATA targets. A useful analogy: one can regard an expander as akin to a [[network switch]] in a network, which connects multiple systems using a single switch port.

SAS 1 defined two types of expander; however, the SAS-2.0 standard has dropped the distinction between the two, as it created unnecessary topological limitations with no realized benefit:
* An ''edge expander'' allows for communication with up to 255 SAS addresses, allowing the SAS initiator to communicate with these additional devices. Edge expanders can do direct table routing and subtractive routing. (For a brief discussion of these routing mechanisms, see below). Without a fanout expander, you can use at most two edge expanders in a delivery subsystem (because you connect the subtractive routing port of those edge expanders together, and you can not connect any more expanders). Fanout expanders solve this bottleneck.
* A ''fanout expander'' can connect up to 255 sets of edge expanders, known as an ''edge expander device set'', letting even more SAS devices be addressed. The subtractive routing port of each edge expanders connects to the phys of fanout expander. A fanout expander cannot do subtractive routing, it can only forward subtractive routing requests to the connected edge expanders.

Direct routing allows a device to identify devices directly connected to it. Table routing identifies devices connected to the expanders connected to a device's own PHY. Subtractive routing is used when you are not able to find the devices in the sub-branch you belong to. This passes the request to a different branch altogether.

Expanders exist to allow more complex interconnect topologies. Expanders assist in link-switching (as opposed to packet-switching) end-devices (initiators or targets). They may locate an end-device either directly (when the end-device is connected to it), via a routing table (a mapping of end-device IDs and the expander the link should be switched to downstream to route towards that ID), or when those methods fail, via subtractive routing: the link is routed to a single expander connected to a subtractive routing port. If there is no expander connected to a subtractive port, the end-device cannot be reached.

Expanders with no PHYs configured as subtractive act as fanout expanders and can connect to any number of other expanders. Expanders with subtractive PHYs may only connect to two other expanders at a maximum, and in that case they must connect to one expander via a subtractive port and the other via a non-subtractive port.

SAS-1.1 topologies built with expanders generally contain one root node in a SAS domain with the one exception case being topologies that contain two expanders connected via a subtractive-to-subtractive port. If it exists, the root node is the expander, which is not connected to another expander via a subtractive port. Therefore, if a fanout expander exists in the configuration, it must be the domain's root node. The root node contains routes for all end devices connected to the domain. Note that with the advent in SAS-2.0 of table-to-table routing and new rules for end-to-end zoning, more complex topologies built upon SAS-2.0 rules do not contain a single root node.

===Connectors===
SAS connectors are much smaller than traditional parallel [[SCSI connector]]s. Commonly, SAS-3 provides for point data transfer speeds up to 12&nbsp;Gbit/s.<ref>{{cite web |url= http://www.scsita.org/library/2013/03/lsi-first-to-ship-new-high-performance-12gbs-sas-products.html |title=LSI First to Ship New High-Performance 12Gb/s SAS Products |work=SCSITA.org |publisher=[[SCSI Trade Association]] |access-date=2013-12-03}}</ref> Currently, SAS-4 is available with up to 24&nbsp;Gbps; with SAS-5 under development, according to [https://www.t10.org/members/w_sas5.htm T10].

The physical SAS connector comes in several different variants:<ref>{{cite web |url= http://ftp.seagate.com/sff/ |title=SFF Committee specifications |work=ftp.Seagate.com |publisher=[[Seagate Technology]] |access-date=2013-08-05}}</ref>

{| class="wikitable sortable" style="text-align:left; vertical-align:top;"
|-
! Code-<br />name<ref>{{Cite web|title=SFF Specifications {{!}} SNIA|url=https://www.snia.org/technology-communities/sff/specifications|access-date=2021-06-06|website=www.snia.org}}</ref>
! other names
! external/<br />internal
! Pins
! No of devices<br />/ lanes
! Comment
! Image
|- style="text-align:left; vertical-align:top;"
| SFF-8086
| Internal mini-SAS,<br />internal mSAS
| internal
| 26
| 4 devices<br>4 lanes
| {{Anchor|SFF-8086}}This is a less common implementation of internal mSAS than SFF-8087's 36-circuit version.<br />The fewer positions is enabled by it not supporting sidebands.
| style="padding: 0" | [[File:SFF 8086.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8087<ref>{{Cite web|title=Mini Multilane 4X Unshielded Connector Shell and Plug, Rev 2.6|url=https://members.snia.org/document/dl/25823|url-status=live|archive-url=https://web.archive.org/web/20190129162758/https://members.snia.org/document/dl/25823|archive-date=January 29, 2019|website=}}</ref><ref>{{Cite web|title=SFF-8087|url=https://cs-electronics.com/sff-8087/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
| Internal mini-SAS,<br />internal mSAS,<br />internal iSAS,<br />internal iPass
| internal
| 36
| 4 devices<br>4 lanes
| {{Anchor|SFF-8087}}Unshielded 36-circuit implementation of SFF-8086.<br />[[Molex connector|Molex]] iPass reduced width internal 4× connector; 12&nbsp;Gbit/s capability.
| style="padding: 0" | [[File:SFF-8087 SMC.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8088<ref>{{Cite web|title=Mini Multilane 4X Shielded Connector Shell and Plug, Rev 3.4|url=https://members.snia.org/document/dl/25824|url-status=live|archive-url=https://web.archive.org/web/20201114131827/https://members.snia.org/document/dl/25824|archive-date=November 14, 2020}}</ref><ref>{{Cite web|title=SFF-8088|url=https://cs-electronics.com/sff-8088/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
| External mini-SAS,<br />external mSAS,<br />external iSAS,<br />external iPass
| external
| 26
| 4 devices<br>4 lanes
| Shielded 26-circuit implementation of SFF-8086.<br />[[Molex connector|Molex]] iPass reduced width external 4× connector; 12&nbsp;Gbit/s capability.
| style="padding: 0" | [[File:SFF 8088.jpg|200px]]
|-
|SFF-8431<ref>{{Cite web|title=SFP+ 10 Gb/s and Low Speed Electrical Interface, Rev 4.1|url=https://members.snia.org/document/dl/25891|url-status=live|archive-url=https://web.archive.org/web/20210606141238/https://members.snia.org/document/dl/25891|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8431 SFP+|url=https://cs-electronics.com/sff-8431/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
|[[SFP+]]
|external
|20
|1 device<br>1 lane
|
|
|- style="text-align:left; vertical-align:top;"
| SFF-8436<ref>{{Cite web|title=QSFP+ 4X 10 Gb/s Pluggable Transceiver, rev 4.9|url=https://members.snia.org/document/dl/25896|url-status=live|archive-url=https://web.archive.org/web/20191226093417/https://members.snia.org/document/dl/25896|archive-date=December 26, 2019}}</ref><ref>{{Cite web|title=SFF-8436|url=https://cs-electronics.com/sff-8436/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
| [[QSFP+]],<br />Quad SFP+
| external
| 38
| 1 device<br>4 lanes
| Commonly used with many [[NetApp]] storage systems.<br />Often seen with SFF-8088 or SFF-8644 on the other end; 6&nbsp;Gbit/s capability.
|
|- style="text-align:left; vertical-align:top;"
| SFF-8470<ref>{{Cite web|title=Shielded High Speed Serial Multilane Copper Connector, Rev 3.3|url=https://members.snia.org/document/dl/25914|url-status=live|archive-url=https://web.archive.org/web/20210606152108/https://members.snia.org/document/dl/25914|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8470|url=https://cs-electronics.com/sff-8470/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
| [[InfiniBand]] CX4<br />connector,<br />Molex LaneLink
| external
| 34
| 4 devices<br>4 lanes
| High-density external connector (also used as an internal connector).
| style="padding: 0" | [[File:SFF 8470.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8482<ref>{{Cite web|title=Serial Attachment 2X Unshielded Connector, Rev 2.5|url=https://members.snia.org/document/dl/25920|url-status=live|archive-url=https://web.archive.org/web/20210606152620/https://members.snia.org/document/dl/25920|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8482|url=https://cs-electronics.com/sff-8482/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
|
| internal
| 29
| 1 device<br>1 lane
| {{Anchor|SFF-8482}}This form factor is designed for compatibility with SATA but can drive a SAS device.<br />A SAS controller can control SATA drives, but a SATA controller cannot control SAS drives. Lower pins (S1-S7, P1-P11) defined as in SATA. Upper pins S8-S14 provide additional lane of data.

The most common connection<ref>{{Cite web|last=servethehome|date=2011-01-31|title=SAS/ SATA SFF-8087, 8088, 8470, 8482, 8484 Connectors Guide|url=https://www.servethehome.com/sas-sata-cables-guide-sff8087-8088-8470-8482-8484-single-device-connectors/|access-date=2021-01-12|website=ServeTheHome|language=en-US}}</ref> for SAS drives connecting to backplanes in servers, i.e. PowerEdge<ref>{{Cite web|title=Compatible Dell PowerEdge Server Hard Drives|url=https://waterpanther.com/collections/compatible-dell-poweredge-server-hard-drives|access-date=2021-01-12|website=Water Panther|language=en-US}}</ref> and ProLiant<ref>{{Cite web|title=Compatible HPE ProLiant Server Hard Drives|url=https://waterpanther.com/collections/compatible-hpe-proliant-server-hard-drives|access-date=2021-01-12|website=Water Panther|language=en-US}}</ref>
| style="padding: 0" | [[File:SFF-8482 SAS Plug - Bokeh at f22.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8484<ref>{{Cite web|title=Multilane Unshielded Serial Attachment Connectors, Rev 2.0|url=https://members.snia.org/document/dl/25922|url-status=live|archive-url=https://web.archive.org/web/20210606152920/https://members.snia.org/document/dl/25922|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8484|url=https://cs-electronics.com/sff-8484/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
|
| internal
| 32 or<br />19
| 4 devices<br>4 lanes
| High-density internal connector, 2 and 4 lane versions are defined by the SFF standard.
| style="padding: 0" | [[File:SFF-8484 straight connector.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| [[SFF-8485]]<ref>{{Cite web|title=SFF-8485 Specification for Serial GPIO (SGPIO) Bus, Rev 0.7|url=https://members.snia.org/document/dl/25923|url-status=live|archive-url=https://web.archive.org/web/20190626094026/https://members.snia.org/document/dl/25923|archive-date=June 26, 2019}}</ref>
|
|
|
|
| Defines [[SGPIO]] (extension of SFF 8484),<br />a serial link protocol used usually for LED indicators.
|
|- style="text-align:left; vertical-align:top;"
| SFF-8613<ref>{{Cite web|title=Mini Multilane 4/8X Unshielded Connector (HDun), Rev 3.5|url=https://members.snia.org/document/dl/25938|url-status=live|archive-url=https://web.archive.org/web/20210606153441/https://members.snia.org/document/dl/25938|archive-date=June 6, 2021}}</ref><br />(SFF-8643<ref>{{Cite web|title=Mini Multilane 4/8X 12 Gb/s Unshielded Connector (HD12un), Rev 3.5|url=https://members.snia.org/document/dl/25951|url-status=live|archive-url=https://web.archive.org/web/20210606153628/https://members.snia.org/document/dl/25951|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8643|url=https://cs-electronics.com/sff-8643/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>)
| Mini-SAS HD,<br />U.2
| internal
| 36
| 1 device<br>4 lanes
| Mini-SAS HD (introduced with SAS 12&nbsp;Gbit/s)

Also known as a U.2 port<ref>{{Cite web|title=ICY TIPs_ICY DOCK manufacturer Removable enclosure, Screwless hard drive enclosure, SAS SATA Mobile Rack, DVR Surveillance Recording, Video Audio Editing, SATA portable hard drive enclosure|url=https://www.icydock.com/knowledge.php?id=70|access-date=2020-06-29|website=www.icydock.com}}</ref> along with SFF-8639.
| style="padding: 0" | [[File:SFF-8643 SMC.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8614<ref>{{Cite web|title=Mini Multilane 4/8X Shielded Cage/Connector (HDsh), Rev 3.4|url=https://members.snia.org/document/dl/25939|url-status=live|archive-url=https://web.archive.org/web/20210606153828/https://members.snia.org/document/dl/25939|archive-date=June 6, 2021}}</ref><br />(SFF-8644<ref>{{Cite web|title=Mini Multilane 4/8X 12 Gb/s Shielded Cage/Connector (HD12sh), Rev 3.5|url=https://members.snia.org/document/dl/25952|url-status=live|archive-url=https://web.archive.org/web/20201112010209/https://members.snia.org/document/dl/25952|archive-date=November 12, 2020}}</ref><ref>{{Cite web|title=SFF-8644|url=https://cs-electronics.com/sff-8644/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>)
| external Mini-SAS HD
| external
| 
| 1 device<br>4 lanes
| Mini-SAS HD (introduced with SAS 12&nbsp;Gbit/s)
| style="padding: 0" | [[File:SFF-8644 cable.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| Sideband<br />connector
| 
| internal
| 
| 
| Often seen with 1× SFF-8643 or 1× SFF-8087 on the other end&nbsp;–<br />internal [[fan-out]] for 4× SATA drives.<br />Connects the controller to drives without backplane or<br />to the (SATA) backplane and optionally, to the status LEDs.
| style="padding: 0" | [[File:Sideband.jpg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8680<ref>{{Cite web|title=Serial Attachment 2X 12 Gb/s Unshielded Connector, Rev 2.1|url=https://members.snia.org/document/dl/25970|url-status=live|archive-url=https://web.archive.org/web/20210606154155/https://members.snia.org/document/dl/25970|archive-date=June 6, 2021}}</ref><ref>{{Cite web|title=SFF-8680|url=https://cs-electronics.com/sff-8680-2/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
|
| internal
| 
| {{unbulleted list|1 |(2 ports)}}
| {{unbulleted list|SAS 12 Gbit/s backplane connector; |same pinout as SFF-8482, but with electrical requirements for 12&nbsp;Gbit/s;| SFF-8678 is analogously defined for 6&nbsp;Gbit/s.}}
| style="padding: 0" |
|- style="text-align:left; vertical-align:top;"
| SFF-8639<ref>{{Cite web|title=Multifunction 6X Unshielded Connector, Rev 2.1|url=https://members.snia.org/document/dl/26489|url-status=live|archive-url=https://web.archive.org/web/20200217083042/https://members.snia.org/document/dl/26489|archive-date=February 17, 2020}}</ref><ref>{{Cite web|title=SFF-8639|url=https://cs-electronics.com/sff-8639/|access-date=2021-06-06|website=CS Electronics|language=en-US}}</ref>
|U.2<ref>{{cite web|title=SFF-8639 Review|url=http://www.pcper.com/news/Storage/Connector-Formerly-Known-SFF-8639-Now-Called-U2|access-date=2016-07-21|work=[[PC Perspective]]|date=8 June 2015 |publisher=TekPerspective}}</ref>
| internal
| 68
| 1 device<br>4 lanes
| {{unbulleted list|SAS 12 Gbit/s backplane connector; |downward-compatible with SFF-8680. }}
| style="padding: 0" | [[File:SFF-8639.jpg|200px]]<br/>[[File:SFF-8639_connector.svg|200px]]
|- style="text-align:left; vertical-align:top;"
| SFF-8638<ref>{{Cite web|title=Multifunction 6X 24 Gb/s Unshielded Connector, Rev 1.1|url=https://members.snia.org/document/dl/25947|url-status=live|archive-url=https://web.archive.org/web/20210606154259/https://members.snia.org/document/dl/25947|archive-date=June 6, 2021}}</ref>
|
|
|
|
| {{unbulleted list|Four 1x ports at up to 24&nbsp;Gb/s each; |two 2x ports at up to 48&nbsp;Gb/s each; |one 4x port at up to 96&nbsp;Gb/s.}}
|
|- style="text-align:left; vertical-align:top;"
| SFF-8640<ref>{{Cite web|title=Serial Attachment 4X 24 Gb/s Unshielded Connector, Rev 1.0|url=https://members.snia.org/document/dl/25949|url-status=live|archive-url=https://web.archive.org/web/20210606154351/https://members.snia.org/document/dl/25949|archive-date=June 6, 2021}}</ref>
|
|
|
|
| {{unbulleted list|Four 1x ports at up to 24&nbsp;Gb/s each; |two 2x ports at up to 48&nbsp;Gb/s each; |one 4x port at up to 96&nbsp;Gb/s.<ref>{{Cite web |url= http://www.scsita.org/content/library/sas_device_to_mid-plane_interconnects_roadmap/ |title=SAS Device to Mid-plane Interconnects Roadmap |date=2015-08-15 |work=SCSITA.org |publisher=[[SCSI Trade Association]] |access-date=2017-10-14}}</ref>}}
|
|- style="text-align:left; vertical-align:top;"
| SFF-8681<ref>{{Cite web|title=Serial Attachment 2X 24 Gb/s Unshielded Connector, Rev 1.0|url=https://members.snia.org/document/dl/25971|url-status=live|archive-url=https://web.archive.org/web/20210606154739/https://members.snia.org/document/dl/25971|archive-date=June 6, 2021}}</ref>
|
|
|
|
| {{unbulleted list|Two 1x ports at up to 24&nbsp;Gb/s each; |one 2x ports at up to 48&nbsp;Gb/s each.}}
|
|-
|SFF-8654<ref>{{Cite web|title=0.6mm 4/8X Unshielded I/O Connector, Rev 1.2|url=https://members.snia.org/document/dl/26744|url-status=live|archive-url=https://web.archive.org/web/20210710095246/https://members.snia.org/document/dl/26744|archive-date=July 10, 2021|access-date=July 10, 2021}}</ref>
|SlimSAS<ref>{{Cite web|title=SAS 4.0, PCI-E 4.0, Upcoming 24Gbps, New HBA's and RAID cards, SlimSAS, My New "Cables" and the new SFF Connector: The Future Is Here, Bois.|url=https://forums.servethehome.com/index.php?threads/sas-4-0-pci-e-4-0-upcoming-24gbps-new-hba%E2%80%99s-and-raid-cards-slimsas-my-new-%E2%80%9Ccables%E2%80%9D-and-the-new-sff-connector-the-future-is-here-bois.32425/|url-status=live|archive-url=https://web.archive.org/web/20210527161518/https://forums.servethehome.com/index.php?threads/sas-4-0-pci-e-4-0-upcoming-24gbps-new-hba%E2%80%99s-and-raid-cards-slimsas-my-new-%E2%80%9Ccables%E2%80%9D-and-the-new-sff-connector-the-future-is-here-bois.32425/|archive-date=May 27, 2021|access-date=2021-07-10|website=ServeTheHome Forums|date=30 March 2021 |language=en-US}}</ref>
|internal
|4X: 38
8X: 74
| 1 device<br>4 lanes
|4X and 8X SAS-4 plug and receptacle
|[[File:Slimsas-x8-male-connector.jpg|200px]]
|}

== {{Anchor|NL-SAS}}Nearline SAS ==
''[[Nearline storage|Nearline]] SAS'' (abbreviated to ''NL-SAS'', and sometimes called ''midline SAS'') drives have a SAS interface, but head, media, and rotational speed of traditional enterprise-class SATA drives, so they cost less than other SAS drives. When compared to SATA, NL-SAS drives have the following benefits:<ref name="snia-deltas">{{cite web
 | url = http://www.snia.org/sites/default/education/tutorials/2007/fall/storage/WillisWhittington_Deltas_by_Design.pdf
 | title = Desktop, Nearline & Enterprise Disk Drives
 | year = 2007 | access-date = 2014-09-22
 | author = Willis Whittington | publisher = [[Storage Networking Industry Association]] (SNIA)
 }}</ref>{{rp|20}}
* Dual ports allowing redundant paths
* Ability to connect a device to multiple computers
* Full SCSI command set
* No need for using [[Serial ATA Tunneling Protocol]] (STP), which is necessary for SATA HDDs to be connected to a SAS [[host adapter|HBA]].<ref name="snia-deltas" />{{rp|16}}
* No need for SATA [[interposer]] cards, which are needed for pseudo&ndash;dual-port high availability of SATA HDDs.<ref name="snia-deltas" />{{rp|17}}
* Larger depth of command queues

==See also==
* [[List of device bandwidths]]
* [[SCSI / ATA Translation]]
* [[Serial Storage Architecture]]
* [[USB Attached SCSI]]

== References ==
{{Reflist}}

== {{Anchor|MULTILINK}}External links ==
{{Commons category|Serial Attached SCSI}}

* [http://www.t10.org T10 committee]
* [http://www.scsita.org/ SCSI Trade Association]
* [http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas2r15.pdf Current draft revision of SAS-2 from T10] (6.83&nbsp;MiB PDF after registration)
* [http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas3r02a.pdf Current draft revision of SAS-3 from T10] (2.8&nbsp; MB PDF after registration)
* [http://www.dell.com/downloads/global/products/pvaul/en/nearline-sas.pdf Seagate whitepaper on Nearline SAS]
* [https://web.archive.org/web/20150501080307/http://www.snia.org/sites/default/files2/SDC2011/presentations/monday/HarryMason_SAS%20_Standards_Technology_Updater1.pdf SAS Standards and Technology Update], [[Storage Networking Industry Association|SNIA]], 2011, by Harry Mason and Marty Czekalski (''MultiLink SAS'' is described on pp.&nbsp;17&ndash;19)
* [http://scsita.org/library/multilink-sas/ MultiLink SAS presentations, press releases and roadmaps] {{Webarchive|url=https://web.archive.org/web/20190101025346/http://www.scsita.org/library/multilink-sas/ |date=2019-01-01 }}, [[SCSI Trade Association]]
* [http://www.stanzabike.net/images/SAS_Docs/SAS_IG.pdf SAS Integrators Guide], SCSI Trade Association, April 2006
* [http://pinoutguide.com/HD/SAS_connector_pinout.shtml Pinouts of SAS SFF-8482 and other connectors]
{{Computer-bus}}
{{Solid-state drive}}

[[Category:Computer storage buses]]
[[Category:SCSI]]
[[Category:Serial buses]]