Hardware

SAS connector - What is it, features and architecture

The connectivity of a computer equipment has gained importance in recent years due to the increase in peripherals. The USB ports without a doubt they are the most important ones today. But there are other lesser known types of ports that are even more important and little known. This is the case of SAS (Serial Attached SCSI) port.

The SAS port is developed for data transfer between storage units and / or floppy disk drives. To explain it more simply, we could say that it is SATA port on steroids. The main difference is that a SAS connector can support several hard drives simultaneously.

10Gtek® Internal SAS / SATA Raid Controller PCI Express Host Bus Adapter for LSI 9211-8I, LSI SAS2008 Chip, 8-Port 6Gb / s, High Profile & Low Profile
  • I / O Controller: LSI SAS 2008 6Gb / s SAS + SATA Controller.
  • Host Bus Type: PCIe 2.0 x8. Also compatible with PCIe 2.0 x16, PCI-Express 3.0 x8, PCI-Express 3.0 x16.
  • Connectors: 2x Mini SAS SFF-8087.
  • Data Transfer Rates: support up to 6.0Gbps SAS 2, SATA III.
  • NOT support hot swapping!

SAS port development

Any current connection port requires some basic parameters: the development is usually open and standard. Usually the connection ports are developed by associations that are supported by the big companies in the industry. What is sought is to develop a single connection system that can be used by everyone, making its implementation and commercialization easy.

SAS is no exception to this. In 1996 the SCSI Trade Association is created1 in order to create a high speed connection port. The association in December 2001 Introduces SAS Port Requirements and Specifications and initiates the promotion of this technology in the industry.

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Subsequently, in May 2002 the parameters of this port are transferred to the Technical Committee T10 for its standardization. In November 2003, the Serial Attached SCSI (SAS) standard was published by ANSI. The first devices based on this standard began to arrive in 2004.

There are three ranges in terms of participation within this grouping by companies in the sector. These companies have different rights and benefits depending on the level of participation. In addition, they collaborate by contributing capital for development, with an annual fee that varies between $ 4.000 and $ 25.000.

The most prominent members are:

  • Sponsored by: Adaptec, Hewlett-Packard, Intel, LSI Logic, Maxtor, Seagate
  • Main: Fujitsu, Hitachi, IBM, Western Digital
  • Promotion: Dell, NEC, Texas Instruments

SAS port features

It is sought with this type of connection to offer the highest possible transfer speed between devices. The great advantage over other types of connectors is that the data transfer interface is done in series. Mainly this type of connection is used in servers, where high performance is required and there are usually many storage units.

For this type of connection there are special storage units with advanced features. It was initially used in special mechanical hard drives that supported between 10.000RPM and 15.000RPM, or what is the same, almost twice the speed of rotation of a commercial hard disk.

hard drive sas front-end

Currently the market is already starting to stop using mechanical hard drives, moving to solid state drives. These are much more efficient and can better exploit the performance of the SAS ports. This port currently achieves transfer speeds of up to 22.5GB / s.

Another feature of SAS ports is that they allow for the installation or removal of drives hot. This is nothing more than putting or removing a hard drive without having to shut down the system. Currently SATA ports also offer this possibility.

Note that SATA hard drives can be plugged into SAS ports, but not the other way around. This is because the SAS port is very similar to the SATA port. While the ports on the motherboard or expansion boards differ slightly, the connector on the storage drive is usually the same.

sas connector cables

Technical aspects of the SAS port

As we have commented, this port has been developed to offer a high data transfer. In addition, it is highly flexible, so it offers ease when developing large storage systems.

These ports have the ability to communicate directly with each other, a great advantage when it comes to data management. The system itself generates a unique and universal number, so there are no conflicts in communication. In addition, in multiple connections it has the ability to maintain a constant transfer for each device

Each SAS port supports up to 16 drives, something that does not happen in the SATA ports, which only support 1 drive. Each tSAS card has a capacity limit of 128 drives and theoretical limit in a system is 65.535 units through expanders.


Small comparison SAS-SATA

SAS versionSAS speedSATA speedSATA version
SAS-13.0Gbit / s1.5Gbit / sSATA I
SAS-26.0Gbit / s3.0Gbit / sSATA II
SAS-312.0Gbit / s6.0Gbit / sSATA III
SAS-422.5Gbit / s--

Note: There is currently no data from a SATA IV interface

difference sas connector and sata connector

SAS parts

Initiator

Source element that manages device service requests and manages tasks for processing by a target device and receives responses for the same requests from other target devices. The initiators can be provided as an integrated component on the motherboard or as an additional host bus adapter.


Object

Device containing logical drives and destination ports that receives job requests. It performs the processing of the requests and sends the response of those requests to the initiating devices. A target drive could be a storage drive or an array of storage drives.


Service delivery subsystem

Part of an I / O system that transmits information between an initiator and a target. Typically cables connecting an initiator and target with or without expanders and backplates, constitute a service delivery subsystem.


Expanders

Device that is part of a service delivery subsystem and facilitates communication between SAS devices. These expanders make it easy to connect multiple end devices to a single initiator port

sas ports

SAS architecture

Physical level

At this level, the electrical and physical characteristics of the connector are defined, as well as the transmission parameters through difference signaling. The characteristics of the passive interconnection are established based on 3 different connectors:

  • SFF-8482: SATA compliant
  • SFF-8484; SFF-8087; SFF-8643: Internal connector for up to 4 devices
  • SFF-8470; SFF-8088; SFF-8644: External connector for up to 4 devices

PHY level

Here the protocol of the different signals is defined. Each of the PHYs has a transceiver and a physical link. It offers 8b / 10b data encoding and 128b / 150b SPL packet encodings.

Note: PHY is short for physical layer o physical layer of integrated circuits. It connects a data link layer to a physical medium, either through metallic cables or through fiber optics.


Link level

The primitive insert and remove elements are set for clock rate mismatch matching. Primitive encoding and data encoding are performed to reduce EMI.

Native connections between SAS targets and initiations, and tunnel connections between SAS initiators and SATA objects connected to Serial Attached SCSI expanders are also established and broken within this level. Finally energy is managed at this level.


Port level

An abstraction that groups together a set of several PHYs and SAS addresses that connect to other PHYs. The PHY layer through which the raster is transferred is selected. It establishes the communication of opening and closing the connections in the link layer of each PHY.


Transport level

Frame connection definition and three different protocols are supported:

  • SSP (SerialSCSIProtocol): Command level communication with SCSI devices
  • STP (Serial Atneling Protocol): Command level communication with SATA devices
  • SMP (Serial Management Protocol): SAS suite management

SAS expanders

Components that facilitate communication between a large number of SAS devices, with these expanders having two or more external expansion ports. The expanders have at least one SAS management protocol destination port and can support SAS drives.

Expanders are not required to interconnect an initiator and SAS targets. At the same time, it enables a single initiator to communicate with more SAS / SATA targets. Its operation is similar to a network switch, allowing multiple systems to be connected using a single switched port.

SAS RAID card

The SAS 1 standard defines two types of expanders, although the SAS 2.0 standard eliminates this distinction, generating topological limitations that do not provide benefits:

  • Edge expander: Generates a communication limit of up to 255 SAS addresses, allowing the SAS initiator to communicate with the other devices. These expanders allow table director routing and subtractive routing. If a deployment expander is lacking, there is a maximum limit of two edge expanders in a delivery subsystem. Fanout expanders solve this bottleneck.
  • Drop-down expander: Connects up to 255 sets of edge expanders, known as set of edge expander devices. This system allows increasing the number of SAS devices. These types of expanders do not have subtractive routing capability, they only forward subtractive routing requests to edge expanders.
sas controller card

Nearline SAS

Nearline SAS drives (abbreviation: NL-SAS) feature a SAS interface but with a header, media, and rotational speed of traditional business-class SATA drives, but at a lower cost than SAS drives. These NL-SAS drives offer the following benefits compared to SATA ports:

  • Dual ports to generate redundant paths
  • Connecting a device to multiple computers
  • Full set of SCSI commands
  • No STP protocol required, required for SATA drives connecting to a SAS HBA
  • No SATA interposer cards required, required for pseudo-dual port high availability of SATA hard drives
  • Greater depth of command queues
hp nl sas drive
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Robert Sole

Director of Contents and Writing of this same website, technician in renewable energy generation systems and low voltage electrical technician. I work in front of a PC, in my free time I am in front of a PC and when I leave the house I am glued to the screen of my smartphone. Every morning when I wake up I walk across the Stargate to make some coffee and start watching YouTube videos. I once saw a dragon ... or was it a Dragonite?

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