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Demartek Storage Interface Comparison

 

Demartek Storage Networking Interface Comparison

Updated 26 August 2019

The Demartek Storage Interface Comparison reference page provides information on interfaces used in computer storage devices including Ethernet, Fibre Channel, FCoE, InfiniBand, iSCSI, NVMe, PCI Express, SAS, SATA, Thunderbolt and USB. This material includes history and roadmaps, comments on data transfer rates, cabling and connectors and more. The goal is to provide IT professionals with a great deal of useful data center infrastructure information in one place.

Special Announcement — SD cards to use NVMe
September 2018 - We have added a new SD Express area in the roadmap section of this document.

We started this reference page in 2010 and update it periodically as we discover new information. As you might imagine, this page has grown over time.

Most of the interface types listed here are known as “block” interfaces, meaning that they provide an interface for “block” reads and writes. They simply provide a conduit for blocks of data to be read and written, without regard to file systems, file names or any other knowledge of the data in the blocks. The host requesting the block access provides a starting address and number of blocks to read or write.

We have produced deployment guides for some of the technologies described in this document.

Also see our Storage Tutorial Videos.

Contents

These are clickable links to locations within this document.

Acronyms

Network throughput rates are generally measured in bits per second. Storage throughput rates are generally measured in bytes per second.

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Storage Networking Interface Comparison Table
Number of Devices Maximum Distance (m) Cable Type Interface Device Transfer Rate (MB/sec) Interface Attributes
FC 16M 10 (copper)
10KM+ (optical)		 Copper
Optical		 HBA 100, 200, 400, 800, 1600, 3200 Dual Port
FCoE 16M 10 (copper)
very long (optical)		 Copper
Optical		 CNA
10GbE NIC		 1150, 4600 Dual Port
IB 48M 15 (copper)
very long (optical)		 Copper
Optical		 HCA 1000, 2000, 4000, 7000, 12,500 full-duplex, Dual Port
iSCSI Many Ethernet cable distance Copper
Optical		 NIC, HBA 100, 1000, 4000  
SAS
(passive)
 16K 10 Copper Onboard, HBA 300, 600, 1200 full-duplex, Dual Port
SAS
(active)
 16K 20 Copper Onboard, HBA 300, 600, 1200 full-duplex, Dual Port
SAS
(active)
 16K 100 Optical Onboard, HBA 300, 600, 1200 full-duplex, Dual Port
SATA 1 1 Copper Onboard, HBA 150, 300, 600 half-duplex, Single Port
Thunderbolt 6 4 Copper Onboard 1000, 2000, 4000  
USB 127 5 Copper, Wireless Onboard, Adapter card 0.15, 1.5, 48, 500, 1000 Single Port

PCIe data rates are provided in the PCI Express section below.

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Transfer Rate

Transfer rate, sometimes known as transfer speed, is the maximum rate at which data can be transferred across the interface. This is not to be confused with the transfer rate of individual devices that may be connected to this interface. Some interfaces may not be able to transfer data at the maximum possible transfer rate due to processing overhead inherent with that interface or the protocol used on that interface. Some interface adapters provide hardware offload functions to improve performance, manageability and/or reliability of the data transmission across the respective interface. The transfer rates listed are across a single port at half-duplex (from point A to point B, one direction at a time).

Bits vs. Bytes and Encoding Schemes

Transfer rates for storage interfaces and devices are generally listed as MB/sec or MBps (MegaBytes per second), which is generally calculated as Megabits per second (Mbps) divided by 10. Many of these interfaces use “8b/10b” encoding which maps 8 bit bytes into 10 bit symbols for transmission on the wire, with the extra bits used for command and control purposes. When converting from bits to bytes on the interface, dividing by ten (10) is exactly correct. 8b/10b encoding results in a 20 percent overhead (10-8)/10 on the raw bit rate.

Beginning in 2010 newer encoding schemes emerged that improve data transfer efficiency. The first of these newer encoding schemes is known as “64b/66b” and is used for 10GbE, 10GbFC (for ISL’s) and 16Gb FC and some of the higher data rates for IB. 64b/66b encoding is not directly compatible with 8b/10b, but the technologies that implement it are built so that they can work with the older encoding scheme. 16Gb Fibre Channel uses a line rate of 14.025 Gbps, but with the 64b/66b encoding scheme results in a doubling of the throughput of 8Gb Fibre Channel, which uses a line rate of 8.5 Gbps with the 8b/10b encoding scheme. 64b/66b encoding results in a 3 percent overhead (66-64)/66 on the raw bit rate.

PCIe versions 1.x and 2.x use 8b/10b encoding. PCIe version 3 uses 128b/130b encoding, resulting in a 1.5 percent overhead on the raw bit rate. Additional PCIe information is provided in the PCI Express section below.

USB 3.1 Gen 2 (10 Gbps) uses use 128b/132b encoding. See Roadmaps section below.

Encoding Scheme Table
Overhead Applications
8b/10b 20% 1GbE, FC (up to 8Gb), IB (SDR, DDR & QDR), PCIe (1.0 & 2.0) SAS, SATA, USB (up to 3.0)
64b/66b 3% 10GbE, 100GbE, FC (10Gb, 16Gb & 32Gb), FCoE, IB (FDR & EDR), Thunderbolt 2
128b/130b 1.5% PCIe 3.0, 24G SAS (likely)
128b/132b 3% USB 3.1 Gen 2 (10 Gbps, see Roadmaps section below)

Fibre Channel Speed Table
Throughput* (MBps) Line Rate (GBaud) Encoding Host Adapter requirements
(dual-port cards)
1GFC 100 1.0625 8b/10b PCI-X
2GFC 200 2.125 8b/10b PCI-X
4GFC 400 4.25 8b/10b PCI-X 2.0 or
PCIe 1.0 x4
8GFC 800 8.5 8b/10b PCIe 1.0 x8 or
PCIe 2.0 x4
16GFC 1600 14.025 64b/66b PCIe 2.0 x8 or
PCIe 3.0 x4
32GFC 3200 28.05 64b/66b PCIe 3.0 x8
* Throughput rates are single direction. For bi-directional (full-duplex) rates, double the data rates.

Fibre Channel speeds are often abbreviated into the form nnGFC, indicating nn Gbps Fibre Channel.

InfiniBand Speed Table
1X data rate * 4X data rate * 12X data rate * Encoding Host Adapter requirements
(dual-port cards)
SDR 2 Gb/s 8 Gb/s 24 Gb/s 8b/10b PCIe 1.0 x8
DDR 4 Gb/s 16 Gb/s 48 Gb/s 8b/10b PCIe 1.0 x16 or
PCIe 2.0 x8
QDR 8 Gb/s 32 Gb/s 96 Gb/s 8b/10b PCIe 2.0 x8
FDR-10*
* Mellanox only		 10.3125 Gb/s 41.25 Gb/s 123.75 Gb/s 64b/66b PCIe 3.0 x8
FDR 13.64 Gb/s 54.55 Gb/s 163.64 Gb/s 64b/66b PCIe 3.0 x8
EDR 25 Gb/s 100 Gb/s 300 Gb/s 64b/66b PCIe 3.0 x16
* Data rates are single direction. For bi-directional (full-duplex) rates, double the data rates.

InfiniBand connections can be aggregated into 4x (4 lanes) and 12x (12 lanes), depending on the application and connector. QSFP and QSFP+ connectors are used for 4x connections, and CXP connectors are typically used for 12x connections. See the Connector Types section below for more details on the connector types. Newer IB speeds have been announced that are described in the Roadmaps section below.

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History

Products became available with the interface speeds listed during these years. Newer interface speeds are often available in switches and adapters long before they are available in storage devices and storage systems.

All the interface speeds listed are single direction, or half-duplex mode (from point A to point B). Some of these interfaces can also operate in bi-directional or full-duplex mode (both directions simultaneously). For bi-directional rates, double the data rates.

PCIe history is provided in the PCI Express section below.

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Roadmaps

These roadmaps include the estimated calendar years that higher speeds may become available and are based on our industry research, which are subject to change. Past history indicates that several of these interfaces are on a three to five year development cycle for the next improvement in speed. It is reasonable to expect that pace to continue.

It usually takes several months after the specification is complete before products are generally available in the marketplace. Typically, test equipment becomes available before end-user products become available. Widespread adoption of those new products takes additional time, sometimes years.

Some of the standards groups are now working on “Energy Efficient” versions of these interfaces to indicate additions to their respective standards to reduce power consumption.

All the interface speeds listed are single direction, or half-duplex mode (from point A to point B). Some of these interfaces can also operate in bi-directional or full-duplex mode (both directions simultaneously). For bi-directional rates, double the data rates.

See the Connector Types section below for additional roadmap information.

Roadmap slides are courtesy of the respective industry organizations.

SAS-SATA Connector Compatibility

SAS-SATA Connector Compatibility
Source: SCSI Trade Association

Express Bay Connector Backplane

Express Bay Connector Backplane
Source: SCSI Trade Association

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Cables: Fiber Optics and Copper

As interface speeds increase, expect increased usage of fiber optic cables and connectors for most interfaces. At higher Gigabit speeds (10Gb+), copper cables and interconnects generally have too much amplitude loss except for short distances, such as within a rack or to a nearby rack. This amplitude loss is sometimes called a poor signal-to-noise ratio or simply “too noisy”.

Fiber-optic cables: Single-mode fiber vs. Multi-mode fiber

There are two general types of fiber optic cables available: single-mode fiber and multi-mode fiber.

Meter-for-meter, single-mode and multi-mode cables are similarly priced. However, some of the other components used in single-mode links are more expensive than their multi-mode equivalents.

When planning datacenter cabling requirements, be sure to consider that a service life of 15 to 20 years can be expected for fiber optic cabling, so the choices made today need to support legacy, current and emerging data rates. Also note that deploying large amounts of new cable in a datacenter can be labor-intensive, especially in existing environments.

There are different designations for fiber optic cables depending on the bandwidth supported.

OM3 and OM4 are multi-mode cables that are “laser optimized” (LOMMF) and support 10 Gigabit per lane and faster applications (Ethernet, Fibre Channel, etc.). For Ethernet, this includes 10GbE and 25GbE technologies. For higher speeds, multiple lanes are bundled together (4 x 10Gbps, 4 x 25Gbps, etc.). See the Connector Types section below for additional detail.

Newer multi-mode OM2, OM3 and OM4 (50 µm) and single-mode OS1 (9 µm) fiber optic cables have been introduced that can handle tight corners and turns. These are known as “bend optimized,” “bend insensitive,” or have “enhanced bend performance.” These fiber optic cables can have a very small turn or bend radius with minimal signal loss or “bending loss.” The term “bend optimized” multi-mode fiber (BOMMF) is sometimes used.

OM5 fiber-optic cable, known as wideband multi-mode fiber (WBMMF), transmits four wavelengths (colors) simultaneously using short wavelength division multiplexing (SWDM) to achieve 100Gbps (4 x 25Gbps) transmission on a single-lane connection. OM5 carries at least four times more capacity than OM4 over the same distance. When configured in four parallel lanes (four sets of fiber), transmission speed can reach 400Gbps.

OS1a and OS2 single-mode fiber optics are used for long distances, up to 10,000m (6.2 miles) with the standard transceivers and have been known to work at much longer distances with special transceivers and switching infrastructure. OS1a replaces OS1, as OS1 is considered a “legacy” product.

Each of the multi-mode and single-mode fiber optic cable types includes two wavelengths. The higher wavelengths are used for longer-distance connections. OM5 supports more than two wavelengths.

Update: 24 April 2012 — The Telecommunications Industry Association (TIA) Engineering Committee TR-42 Telecommunications Cabling Systems has approved the publication of TIA-942-A, the revised Telecommunications Infrastructure Standard for Data Centers. A number of changes were made to update the specification with respect to higher transmission speeds, energy efficiency and harmonizing with international standards. For backbone and horizontal cabling and connectors, the following are some of the important updates:

Update: June 2017 — The TIA approved for publication the TIA-942-B data center cabling standard at its June 2017 meeting. This standard includes several updates from Revision-A including:

The TIA-942-B standard was published in July 2017.

Ethernet Fiber-Optic Cables

Indoor vs. Outdoor cabling

Indoor fiber-optic cables are suitable for indoor building applications. Outdoor cables, also known as outside plant or OSP, are suitable for outdoor applications and are water (liquid and frozen) and ultra-violet resistant. Indoor/outdoor cables provide the protections of outdoor cables with a fire-retardant jacket that allows deployment of these cables inside the building entrance beyond the OSP maximum distance, which can reduce the number of transition splices and connections needed.

Fiber Optic Cable Characteristics
Mode Core Diameter Wavelength Modal Bandwidth Cable jacket color
OM1* multi-mode 62.5 µm 850 nm
1300 nm		 200 MHz Orange
OM2* multi-mode 50 µm 850 nm
1300 nm		 500 MHz Orange
OM3 multi-mode 50 µm 850 nm
1300 nm		 2000 MHz Aqua
OM4 multi-mode 50 µm 850 nm
1300 nm		 4700 MHz Aqua
OM5 wideband multi-mode 50 µm 850 - 953 nm 4700 - 2470 MHz Lime Green
OS1* & OS1a
 single-mode 9 µm 1310 nm
1550 nm		 — Yellow
* OM1, OM2 and OS1 are not supported for new installations.

Fiber Optic Cable by Distance and Speed
(single lane)
OM1* OM2* OM3 OM4 OM5
1 Gb/s 300m 500m 860m    
2 Gb/s 150m 300m 500m    
4 Gb/s 70m 150m 380m 400m  
8 Gb/s 21m 50m 150m 190m  
10 Gb/s 33m 82m 300m 400m 400m
16 Gb/s 15m¹ 35m 100m 125m 125m
25 Gb/s — — 70m 100m 100m
32 Gb/s — — 70m 100m 100m
50 Gb/s — — 70m 100m 100m
64 Gb/s — — 70m 100m 100m
* OM1 and OM2 are not supported for new installations.

¹ OM1 cable is not recommended for 16GFC, but is expected to operate up to 15m.

Distances supported in actual configurations are generally less than the distance supported by the raw fiber optic cable. The distances shown above are for 850 nm wavelength multi-mode cables. The 1300 nm wavelength multi-mode cables can support longer distances.

Copper cables: Active Copper vs. Passive Copper

Copper cables are available in passive and active designs. Passive copper cables consume no power and have shorter reach. Active copper cables include components that boost the signal, reduce the noise and work with smaller-gauge cables, improving signal distance, cable flexibility and airflow. These active copper cables consume some power and are more expensive than passive copper cables. From a distance perspective, active copper cables reach longer than passive copper but shorter than fiber-optic cables. The copper cables, both passive and active, typically include a connector or transceiver mounted directly on the cable.

Passive copper cables are very common in datacenters and are frequently used in configurations with top-of-rack (“TOR”) switches because even at the higher speeds, passive copper cables can usually reach the full height of a rack. Many newer datacenters are designed in such a way to keep cable lengths short to take advantage of lower-cost passive copper cables rather than use more expensive active copper cables.

The newer speeds of some interfaces are expected to increase the use of active copper cables over time.

Copper cables: Distances

Passive copper cables, depending on the rated speed, typically are in the single-digit meters in terms of distance. Active copper cables can typically reach into the low double-digits of meters. As the data rates increase, the distance decreases. With single-lane data rates of 25 Gbps and 32 Gbps, copper cables have a relatively short reach.

Research is being conducted to determine the feasibility of copper cables at 100 Gbps per lane. One example of this was shown at DesignCon 2016. An incubation startup company demonstrated a 100 Gbps serial data communication over a 1.5 meter twinaxial copper cable. Additional information is available at www.bifast.io.

Copper: 10GBASE-T and 1000BASE-T

1000BASE-T cabling is commonly used for 1Gb Ethernet traffic in general, and 1Gb iSCSI for storage connections. This is the familiar four pair copper cable with the RJ45 connectors. Cables used for 1000BASE-T are known as Cat5e (Category 5 enhanced) or Cat6 (Category 6) cables.

10GBASE-T cabling supports 10Gb Ethernet traffic, including 10Gb iSCSI storage traffic. The cables and connectors are similar to, but not the same as the cables used for 1000BASE-T. 10GBASE-T cables are Cat6a (Category 6 augmented), also known as Class EA cables. These support the higher frequencies required for 10Gb transmission up to 100 meters (330 feet). Cables must be certified to at least 500MHz to ensure 10GBASE-T compliance. Cat7 (Category 7, Class F) cable is also certified for 10GBASE-T compliance, and is typically deployed in Europe. Cat6 cables may work in 10GBASE-T deployments up to 55m, but should be tested first. 10GBASE-T cabling is not expected to be deployed for FCoE applications in the near future. Some newer 10GbE switches support 10GBASE-T (RJ45) connectors.

10GBASE-CR — Currently, the most common type of copper 10GbE cable is the 10GBASE-CR cable that uses an attached SFP+ connector, also known as a Direct Attach Copper (DAC). This fits into the same form factor connector and housing as the fiber optic cables with SFP+ connectors. Many 10GbE switches accept cables with SFP+ connectors, which support both copper and fiber optic cables. These cables are available in 1m, 3m, 5m, 7m, 8.5m and longer distances. The most commonly deployed distances are 3m and 5m.

10GBASE-CX4 — These cables are older and not very common. This type of cable and connector is similar to cables used for InfiniBand technology.

USB Type-C Cables
Information on the new USB Type-C cables is located in the Roadmaps section above.

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Connector Types

Several types of connectors are available with cables used for storage interfaces. This is not an exhaustive list but is intended to show the more common types. Each of the connector types includes the number of lanes (or channels) and the rated speed. The speeds listed are across a single port at half-duplex (from point A to point B, one direction at a time).

Single Lane Speed

As of early 2011, the fastest generally available connector speeds supported were 10 Gbps per lane. Significantly higher speeds are currently achieved by bundling multiple lanes in parallel, such as 4x10 (40 Gbps), 10x10 (100 Gbps), 12x10 (120 Gbps), etc. Most of the current implementations of 40GbE and 100GbE use multiple lanes of 10GbE and are considered “channel bonded” solutions.

14 Gbps per lane connectors appeared in the last half of 2011. These connectors support 16Gb Fibre Channel (single-lane) and 56Gb (FDR) InfiniBand (multi-lane).

25 Gbps per lane connectors began to appear in volume in 2016. The underlying technology (“25G/28G”) used for 25 Gbps connectors for Ethernet is essentially the same as the technology used for 32Gb Fibre Channel. The Ethernet implementation provides 25 Gbps per lane and the Fibre Channel implementation provides 32 Gbps per lane. This same technology is bundled into four-lane (“quad”) configurations to achieve 100GbE and 128GFC. Other variations of bundling multiple lanes of 25 Gbps may be possible, such as 10x25 (250 Gbps), 12x25 (300 Gbps) or 16x25 (400 Gbps).

In March 2018, Demartek published the Demartek 25GbE Deployment and Installation Tips that provides practical information for deploying 25GbE technology.

With the announcement of 25 Gbps Ethernet, some in the industry believe that single-lane 25 Gbps Ethernet infrastructure (cables, connectors and adapters) will gain faster market acceptance than multi-lane 40 Gbps Ethernet infrastructure.

50 Gbps per lane — The 50 Gb/s, 100 Gb/s, and 200 Gb/s Ethernet Task Force, also known as IEEE 802.3cd, has been working on the 50 Gbps per lane (and higher) standard for Ethernet. This specification is expected to be completed in the second half of calendar year 2018. Some elements of this standard will be used in the Fibre Channel standards. As a result, the Ethernet and Fibre Channel standards will appear more synchronized with each other than in the past. Elements of the single-lane 50GbE standard will be used in the single-lane 64Gb Fibre Channel standard, elements from the single-lane 100GbE standard in the single-lane 128Gb Fibre Channel standard, etc. The first single-lane 50GbE products may appear in hyperscale datacenters as early as the end of 2018.

Some of the faster Ethernet speeds, such as 200 Gb/s and 400 Gb/s may require systems that support PCIe 4.0 or 5.0 technology. For example, a 400GbE adapter requires a PCIe 5.0 x16 slot. See the PCI Express section below for details.

Connector Styles

Two of the popular fiber-optic cable connectors are the SFP-style and the QSFP-style (see diagrams below). SFP stands for “small form-factor pluggable” and QSFP is “quad small form-factor pluggable.” As the data rates for various interfaces have increased, the internal technology in these connectors has changed, and the names have changed slightly. The table below indicates the name of the technology and the interfaces that use it. See the Roadmaps section above for additional details on particular interfaces.

In the first half of 2017, the Ethernet IEEE 802.3cd Standards Committee voted to simultaneously include MicroQSFP, OSFP and QSFP-DD interconnect modules to provide solutions to provide more lanes of connectivity in the same or less space than current SFP and QSFP technology. Each of these attempts to address density, power and thermal issues slightly differently. Any or all of these may become adopted over the coming months and years.

MicroQSFP: The micro Quad Small Form-Factor Pluggable (MicroQSFP or µQSFP) specification provides a compact connector system for four input/output (I/O) electrical channels in the same width as today’s single-lane SFP specification. It supports direct attach copper assemblies, optical modules and active optical cable assemblies. Revision 2.4 of the MicroQSFP specification was released in January 2017. Additional information, including a Frequently Asked Questions page is available on the microQSFP website.

OSFP: The Octal Small Form Factor Pluggable (OSFP) provides eight high speed electrical lanes that will initially support 400 Gbps (8x50G) in a form factor that is slightly wider and deeper than the traditional QSFP technology. Revision 1.11 of the OSFP specification was released in June 2017. Additional information is available on the OSFP website.

QSFP-DD: The Quad Small Form Factor Double Density (QSFP-DD) specification was released in March 2017. This specification is for a new module and cage/connector system similar to, and backward compatible with, the existing QSFP (and QSFP28), but with an additional row of contacts for an eight-lane electrical interface. A number of major industry companies are promoters and contributors to this specification. There is a Frequently Asked Questions section on the main page of the QSFP-DD website.

Development of on-board optical connections is underway via the Consortium for On-Board Optics (COBO).

SFP QSFP Connector/Interface Table
SFP SFP+ SFP28 QSFP+ QSFP28*
Ethernet 1GbE 10GbE 25GbE 40GbE 100GbE
Fibre Channel 1GFC, 2GFC, 4GFC 8GFC, 16GFC 32GFC — 128GFC
InfiniBand — — — QDR, FDR EDR

* QSFP28 is also known as QSFP100 for some 100Gb (4 x 25) Ethernet applications.

Note the encoding schemes described above for additional detail on speeds available for various connector and cable combinations.

Connector Table
Type Lanes Max. Speed per lane (Gbps) Max. Speed total (Gbps) Cable type Usage
Mini SAS SAS 4 6 24 Copper 3Gb, 6Gb SAS
Mini SAS HD SAS 4, 8 12 48, 96 Copper 6Gb, 12Gb SAS
Copper CX4 CX4 4 5 20 Copper 10Gb Ethernet,
SDR and DDR InfiniBand
Small Form-factor Pluggable SFP 1 4 4 Copper, Optical 1Gb Ethernet,
Fibre Channel: 1, 2, 4Gb
Small Form-factor Pluggable enhanced SFP+ 1 16 16 Copper, Optical 10Gb Ethernet, 8Gb & 16Gb Fibre Channel,
10Gb FCoE
Small Form-factor Pluggable 28 SFP28 1 32 32 Copper, Optical 25Gb Ethernet, 32Gb Fibre Channel
Quad Small Form-factor Pluggable QSFP 4 5 20 Copper, Optical Various
Quad Small Form-factor Pluggable enhanced QSFP+ 4 16 64 Copper, Optical 40Gb Ethernet,
DDR, QDR & FDR InfiniBand,
64Gb Fibre Channel
Quad Small Form-factor Pluggable 28 QSFP28 4 32 128 Copper, Optical 100Gb Ethernet,
EDR InfiniBand,
128Gb Fibre Channel
CXP CXP 10, 12 10 100, 120 Copper 100Gb Ethernet,
120Gb other
CFP CFP 10 10 100 Optical 100Gb Ethernet

PCIe data rates and connector types are provided in the PCI Express section.

Connector Diagrams
Type Diagram
Mini SAS SAS
Mini SAS HD SAS HD
Copper CX4 CX4
Small Form-factor Pluggable SFP, SFP+, SFP28
Quad Small Form-factor Pluggable QSFP, QSFP+, QSFP28

PCIe connector types are provided in the PCI Express section.

Demartek mini-SFP photo Mini SFP

In the second half of 2010, a new variant of the SFP/SFP+ connector was introduced to accommodate the Fibre Channel backbone with 64-port blades and the planned increased density Ethernet core switches. This new connector, known as mSFP, mini-SFP or mini-LC SFP, narrows the optical centerline of a conventional SFP/SFP+ connector from 6.25 mm to 5.25 mm. Although this connector looks very much like a standard SFP style connector, it is narrower and is required for the higher-density devices. The photo at the right shows the difference between mini-SFP and the standard size.

CXP and CFP

The CXP (copper) and CFP (optical) connectors are expected to be used initially for switch-to-switch connections. These are expected for Ethernet and may also be used for InfiniBand. CFP connectors currently support 10 lanes of 10 Gbps connections (10x10) that consume approximately 35-40 watts. CFP2 is a single board, smaller version of CFP that also supports 10x10 but uses less power than CFP. During 2013, quite a bit of development activity is focused on CFP2. A future CFP4 connector is in the planning stages that is expected to use the 25/28G connectors and support 4x25. CFP4 is expected to handle long range fiber optic distances.

Mini SAS and Mini SAS HD

The Mini SAS connector is the familiar 4-lane connector available on most SAS cables today. The Mini SAS HD connector provides twice the density as the Mini SAS connector, and is available in 4-lane and 8-lane configurations. The Mini SAS HD connector is the same connector for passive copper, active copper and optical SAS cables. The diagrams below compare these two types of SAS connectors.
Mini SAS HD Receptacle Comparison Mini SAS HD Comparison
Source: SCSI Trade Association

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PCI Express (PCIe)

PCI Express®, also known as PCIe®, stands for Peripheral Component Interconnect Express and is the computer industry standard for the I/O bus for computers introduced in the last few years. The first version of the PCIe specification, 1.0a, was introduced in 2003. Version 2.0 was introduced in 2007 and version 3.0 was introduced in 2010. These versions are often identified by their generation (“gen 1”, “gen 2”, etc.). It can take a year or two between the time the specification is introduced and general availability of computer systems and devices that use the new version of the PCIe specification.

The PCIe specifications are developed and maintained by the PCI-SIG® (PCI Special Interest Group). PCI Express and PCIe are registered trademarks of the PCI-SIG.
PCIe Technology Roadmap

PCIe 2.0 — Servers that have PCIe 2.0 x8 slots can support two ports of 10GbE or two ports of 16GFC on one adapter.

PCIe 3.0 — On 6 March 2012, the major server vendors announced their next generation servers that support PCIe 3.0, which, among other things, doubles the I/O throughput rate from the previous generation. These servers also provide up to 40 PCIe 3.0 lanes per processor socket, which is also at least double from the previous server generation. Workstation and desktop computer motherboards that support PCIe 3.0 first appeared in late 2011. PCIe 3.0 graphics cards appeared in late 2011. Other types of adapters supporting PCIe 3.0 were announced in 2012 and 2013. The PCIe 3.0 specification was completed in November 2010.

PCIe 3.1 — The PCIe 3.1 specification was released in October 2014. It incorporates M-PCIe and consolidates numerous protocol extensions and functionality for ease of access.

PCIe 4.0 — The PCIe 4.0 specification maintains backward compatibility with previous generations of the PCIe architecture such as PCIe 1.x, 2.x and 3.x. In October 2017, the PCIe 4.0, Version 1.0 specification was released. It may take up to a year or more for products that support the PCIe 4.0 architecture to become generally available.

PCIe 5.0 — The PCI-SIG announced that the PCIe 5.0 specification was completed in May 2019. As with previous generations of the PCIe specification, it may take a year or more before products that support the new specification become generally available to the public. Typically, test equipment that conforms to the new specfication becomes available not long after the specification is complete, followed months later by end-user products.

PCIe 6.0 — In June 2019, PCI-SIG announced that 64 GT/s per lane is the next progression in speed for the PCIe 6.0 architecture. The PCI-SIG estimates that they will complete the PCIe 6.0 specification in 2021.

Data rates for different versions of PCIe are shown in the table below. PCIe data rates are expressed in Gigatransfers per second (GT/s) and are a function of the number of lanes in the connection. The number of lanes is expressed with an “x” before the number of lanes, and is often spoken as “by 1”, “by 4”, etc. PCIe supports full-duplex (traffic in both directions). The data rates shown below are in each direction. Note the explanation of encoding schemes described above.

PCIe Data Rate Table*
GT/s Encoding x1 x2 x4 x8 x16
PCIe 1.x 2.5 8b/10b 250 MB/s 500 MB/s 1 GB/s 2 GB/s 4 GB/s
PCIe 2.x 5 8b/10b 500 MB/s 1 GB/s 2 GB/s 4 GB/s 8 GB/s
PCIe 3.x 8 128b/130b 1 GB/s 2 GB/s 4 GB/s 8 GB/s 16 GB/s
PCIe 4.x 16 128b/130b 2 GB/s 4 GB/s 8 GB/s 16 GB/s 32 GB/s
PCIe 5.x 32 128b/130b 4 GB/s 8 GB/s 16 GB/s 32 GB/s 64 GB/s
PCIe 6.x 64 128b/130b? 8 GB/s 16 GB/s 32 GB/s 64 GB/s 128 GB/s
* half-duplex speeds (approximate)

Demartek M.2 photo M.2 — M.2 is the next generation PCIe connector that can be used for internally mounted devices such as boot drives in a variety of devices, from mobile to server. Its multiple socket definitions support WWAN, SSD and other applications. M.2 can support PCIe protocol or SATA protocol, but not both at the same time on the same device. M.2 supports a variety of board width and length options. M.2 is available in single-sided modules that can be soldered down, or single-sided and dual-sided modules used with a connector. M.2 PCIe is also available in a Ball Grid Array (BGA) form factor.

Mini-PCIe — PCI Express cards are also available in a mini PCIe form factor. This is a special form factor for PCIe that is approximately 30mm x 51mm or 30mm x 26.5mm, designed for laptop and notebook computers, and equivalent to a single-lane (x1) PCIe slot. A variety of devices including WiFi modules, WAN modules, video/audio decoders, SSDs and other devices are available in this form factor.

U.2 — U.2 (formerly SFF-8639) is the I/O backplane connector designed for high-density SSD storage devices and is backward compatible with existing storage interfaces. SFF-8639 supports PCIe/NVMe, SAS and SATA devices and enables hot plug and hot swap of devices while the system is running.

Demartek SFF-8639 photo

U.3 — U.3 is the common name for a new type of backplane connector that conforms with the SFF-TA-1001 specification. SFF-TA-1001 Rev. 1.0 was ratified in November 2017 and Rev. 1.1 was ratified in May 2018. The U.3 standard defines a common bay type and connector for SAS, SATA, and NVMe devices enabling single, dual, and wide-port SAS, SATA, and x1, x2 or x4 NVMe devices to all work on the same shared signals and connectors. U.3 is backward compatible with U.2, also known as SFF-8639. With U.3, the locations of the SAS devices and NVMe devices are now in the same physical location, allowing NVMe SSDs to leverage the same backplane infrastructure as SAS and SATA devices and reducing the cost to produce such a backplane. It is expected that backplanes supporting the U.3 specification will allow NVMe, SAS and SATA devices to be intermixed in the backplane, rather than having separate drive bays for NVMe SSDs. U.3 backplanes are expected to appear in servers and other compute platforms possibly by late 2019.

Demartek U.2 & U.3 backplane comparison

M-PCIe™ — M-PCIe is the specification that maps PCIe over the MIPI® Alliance M-PHY® technology used in low-power mobile and handheld devices. M-PCIe is optimized for RFI/EMI requirements and supports M-PHY gears 1, 2 and 3 and will be extended to support gear 4.

I/O Virtualization (SR-IOV & MR-IOV) — In 2008, the PCI-SIG announced the completion of its I/O Virtualization (IOV) suite of specifications including single-root IOV (SR-IOV) and multi-root IOV (MR-IOV).

PCIe External Cables —The concept of sharing PCIe devices or providing access to PCIe devices that may be physically larger than some smaller form-factor systems can accommodate has led to the development of external connections to some PCIe devices. Cables have been developed for extending the PCIe bus outside of the chassis holding the PCIe slots. These cables are specified by indicating the number of PCIe lanes (x4, x8, etc.) supported. Cables are typically available for x4, x8 and x16 lane configurations. Common cable lengths are 1m and 3m. The photo below shows some PCIe cables and connectors. PCIe can also be carried over fiber-optic cables for longer distances. In the future we will begin to see the shift from PCIe cables and connectors to OCuLink cables and connectors, also shown in the image below.

OCuLink — OCuLink is intended to be a low-cost, small cable form factor for PCIe internal and external devices such as storage devices or graphics adapters, offering bit rates starting at 8 Gbps, with headroom to scale, and new independent cable clock integration. OCuLink supports x1, x2 and x4 lanes of PCIe 3.0 connectivity. OCuLink supports passive cables capable of reaching up to 2—3 meters and active copper and optical cables. Active copper cables can reach up to 3—10 meters while active optical cables can reach up to 300 meters in length. The OCuLink specification Revision 1.0 was published in October 2015 and is available to PCI-SIG members via the online specification library.

PCIe and OCuLink cables

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The original version of this page is available at www.demartek.com/Demartek_Interface_Comparison.html on the Demartek website.