History of Storage Interfaces

Data interfaces are evolving so rapidly that it is difficult for storage vendors to keep up with them. Every year there are interfaces that allow you to achieve data transfer speeds many times greater than existing devices. Switches and network adapters begin to support the latest high-speed interfaces long before they become available in storage systems.

The table below shows the evolution of the bandwidth of storage connectivity interfaces in the timeline.

Interface development trends

The following describes the estimated years of new data rates for various interfaces, based on industry research. History shows that for many interfaces, the cycle of developing new standards is 3-4 years.

It is worth noting that from the moment the specification of a new interface is approved and until the appearance on the market of products that support it, it usually takes several months. Widespread adoption of the new standard could drag on for several years.

Work is also underway to develop versions of existing interfaces with reduced power consumption.

Fibre Channel

32Gbps FC (32GFC)

Work on the 32GFC standard, FC-PI-6, began in early 2010. In December 2013, the Fibre Channel Industry Association (FCIA) announced the completion of work on the specification. Products supporting this interface are expected to hit the market in 2015 or 2016. The 32GFC will use a 25/28G SFP+ connector.

The 128Gb MULTI-channel FC interface, known as 128FCp (Parallel Quad Channel), is based on 32Gb FC technology and has been added to the official FC standard development plan. The T11 Committee named the project FC-PI-6P. The completion of the specification is planned for the end of 2014 - the beginning of 2015, the products will be available in 2015 or 2016. The 128GFCp is likely to use QSFP+ connectors, and it is also possible to support CFP2 or CFP4 connectors.

Some manufacturers introduce 32GFC and 128GFC as "Gen 6" Fibre Channel, as this version supports 2 different data rates in two different configurations (serial and parallel).

64Gbps FC (64GFC), 256Gbps FC (256GFC)

The development of the 64GFC and 256GFC standards began in the FC-PI-7 project. Technical stability is expected in 2017. Each revision of FC is backward compatible with at least two previous generations.

FC as a SAN interface

Apparently, Fibre Channel in the foreseeable future will remain the main technology for building SAN networks. Over the years, significant funds (billions of US dollars) have been invested in FC infrastructure, mainly in data centers that will be operational for many more years.

FC as a disk interface

Fibre Channel as an interface for connecting disks is becoming a thing of the past as enterprise-class drive manufacturers move to 6Gbps SAS and 12Gbps SAS. Due to the fairly large volume of 3.5-inch FC drives used in enterprise disk subsystems, it is expected that FC will be used for some time to support them. Among the 2.5-inch drives, the Fibre Channel interface will likely be available on a very small number of devices.

Fibre Channel over Ethernet

FCoE (FC-BB-6)

Work on the FC-BB-6 standard was completed by the T11 committee in August 2014. FC-BB-6 standardizes the VN2VB architecture and improves Domain_ID scalability.

VN2VN is a way to directly connect FCoE (Virtual N_Ports) end nodes without the need for FC or FCoE (FC Forwarders) switches, simplifying configuration in small locations. This idea is sometimes referred to as "Ethernet Only" FCoE. In such networks, zoning is not required, which gives less complexity and reduces costs.

Domain_ID scalability (Domain_ID Scalability) allows FCoE factories to scale to larger SANs.

40Gbps and 100Gbps

40Gbps FCoE is a year or two away. Perhaps the interface will appear simultaneously with 32Gb FC. The IEEE 802.3ba 40Gbps and 100Gbps Ethernet standards were ratified in June 2010. New products should appear after a while.

Most likely, 40Gbps and 100Gbps FCoE, based on the 2010 Ethernet standards, will be used initially for ISL cores, thereby leaving 10Gb FCoE mainly for end connections. It is expected that future versions of 100GFCoE cables and connectors will be available in 10x10 and then 4x25 configurations.

InfiniBand

Currently, products using 100Gbps Infiniband EDR (Enchanced Data Rate) are already available for sale. EDR uses 25/28G SFP+ connectors, as well as Ethernet and Fibre Channel interfaces.

InfiniBand High Data Rate (HDR), which supports speeds 2 times greater than EDR, is expected in 2017 or 2018. HDR host adapters may require PCIe 4.0 slots.

Ethernet

In July 2014, 2 different industry groups—the 20G/50G Ethernet Consortium and the IEEE 802.3 25Gb/s Ethernet Study Group—announced new work on the Ethernet specification to take advantage of 25Gb PHY in a single-band configuration. The result was a single-band specification similar to the existing 10GbE technology, but 2.5 times faster. Products that use these technologies are already available. It is also planned to develop a 50GbE standard that uses 2 25GbE lanes. Completion of the specification is planned in 2018-2020.

The 2.5GbE and 5GbE standards are in development to increase network capacity at no additional cost through the use of Category 5e cables. The NBASE-T Alliance has released version 1.1 of the NBASE-T specification, which describes the implementation at the physical layer. The Technical Working Group is working on a specification for the PHY-MAC system interface, magnetic and channel characteristics. In addition, employees of 25 companies participate in the development of IEEE 802.3bz 2.5/5GBASE-T standards. Products that support 2.5GbE and 5GbE are already on the market.

SAS

12Gbps SAS

The SAS 3 specification, which includes 12Gbps SAS, was sent to INCITS in Q4 2013. End-user 12Gbps SAS products began to appear in the second half of 2013, including SSDs, network adapters (SAS HBAs), and RAID controllers. 12Gbps SAS allows you to take full advantage of the PCIe 3.0 bus.

24Gbps SAS

The 24Gbps SAS interface specification is currently in development. According to forecasts, the first components using 24Gbps SAS may appear in 2016 or 2017, the first products for users will be available in 2018. 24Gbps SAS is designed to be fully compatible with 12Gbps and 6Gbps SAS. A different coding scheme may be used.

Prototypes of the 24Gbps SAS interface will use PCIe 3.x technology, however, it is likely that the final products will use PCIe 4.x technology.

SCSI Express

SCSI Express implements the well-known SCSI protocol over the PCI Express interface, reducing latency by using PCIe. It is designed to match the improved speed of SSD drives. SCSI Express uses the SCSI over PCIe (SOP) and PCIe Queueing Interface (PQI) protocols to create the SOP-PQI protocol. The controllers connect to devices using the SFF-8639 connector, which supports a variety of protocols and interfaces such as PCIe, SAS, and SATA. SCSI Express supports PCIe devices that use up to 4 lanes.

SCSI Express was first proposed in 2011 and adopted as a formal project in 2012, but did not develop until 2015. It is not yet known when the first SCSI Express products will be released to the market.

SAS Connectivity

New SAS connectivity enables data transmission over long distances through the use of active copper patch cords and fiber optic cables. The Mini SAS HD header (SFF-8644) can be used for 6Gbps SAS and 12Gbps SAS.

Future features such as support for the Zoned Block Commands (ZBC) command set and Shingled Magnetic Recording (SMR) larger disc recording technologies are expected.

SATA Express

The SATA Express specification is included in SATA version 3.2. SATA Express allows SATA and PCIe client solutions to coexist. SATA Express allows for faster transfer speeds of up to 2 PCIe lanes (2GBps for PCIe 3.0 and 1GBps for PCIe 2.0) compared to current SATA technology (0.6GBps). This speed is suitable for SSDs and SSHDs, while ordinary HDDs can continue to use the existing SATA interface. Each device can use the PCIe or SATA connector, but not both. The individual signal generated by the device, tells the host, is a SATA or PCI Express device. As of mid-2015, SATA Express is supported by a very small number of motherboards. While it is not clear whether SATA Express will be adopted by the market, in the near future we should not expect the appearance of a large number of products.

What's New in SATA

New features planned for the future include enterprise-grade options such as remote power off, improved array recovery, and optimizations for NAND Flash devices. It is also planned to support SMR (Shingled Magnetic Recording) technology.

Thunderbolt

Thunderbolt 2 was introduced at the end of 2013, now there are many devices that use this interface. The data transfer rate of Thunderbolt 2 is 20 Gbps.

Thunderbolt 3 (40 Gbps) was announced in June 2015. A USB type-C cable is used, which supports USB 3.1 (10 Gbps), Display Port (dual 4k displays), 4 lanes PCI Express 3.0 and previous versions of Thunderbolt. In addition, 15 watts are provided to power connected devices and USB power is supported to charge laptop computers up to 100 watts. Active copper and fiber optic cables support data rates of up to 40 Gbps. Less expensive passive copper cables support speeds of up to 20 Gbps. The first products using Thunderbolt 3 are expected to appear in late 2015. Many more devices will be available in 2016.

USB

USB 3.1

In July 2013, the USB 3.0 Promoter Group announced the creation of the USB 3.1 specification. The new interface allows you to work at a speed of 10 Gbps and is fully compatible with previous versions of USB. USB 3.1 uses a 128b/132b encoding scheme in which 4 bits are used to control the protocol and transmit cable information. Devices that use USB 3.1 with the new Type-C cable are already on the market.

USB Power Supply

USB is an interface with the ability to power connected devices and there are more and more devices charging or running from USB. The USB Power Delivery (PD) specification version 1.0 was introduced in July 2012. It proposed to increase the power supply from 7.5 watts to 100 watts, depending on the type of cable and connector. The devices must agree with each other to determine the voltage and amperage for the transmission of electricity, and it is possible to transmit energy in any direction. Devices can adjust the power supply during the transmission of information. Prototypes of devices with USB PD began to appear in late 2013. The USB PD specification is included in the USB 3.1 specification.

USB Type-C cable

Specification of the new cable and connector was completed in August 2014. This cable has a significantly different design with a reduced connector size, which can easily be used in various devices. In accordance with the new specification, the cable and connector can be used in any position, regardless of the orientation of the connector and the direction of the cable. The cable has the same type of connector on both sides. The first Type-C USB cables are passive copper cables up to 1 m in length, and active copper and fiber optic cables are expected to appear soon.