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Demartek Storage Networking Interface Comparison

Updated 16 July 2010

Because of the number of interfaces and related technologies that are used for storage devices, we have compiled this summary document providing some basic information for each of the interfaces. This document will be updated periodically. This document may become larger over time. Contact us if you’d like to see additional information in this document.

The interfaces 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.

Contents

Acronyms

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 Dual Port
FCoE 16M 10 (copper)
very long (optical)		 Copper
Optical		 CNA
10GbE NIC		 1000 * Dual Port
IB 16M 15 (copper)
very long (optical)		 Copper
Optical		 HCA 1000, 2000, 4000 Full Duplex, Dual Port
iSCSI Many Ethernet cable distance Copper
Optical		 NIC, HBA 100, 1000  
SAS
(passive)
 16K 10 Copper Onboard, HBA 300, 600 Full Duplex, Dual Port
SAS
(active)
 16K 20 Copper Onboard, HBA 300, 600 Full Duplex, Dual Port
SAS
(active)
 16K 100 Optical Onboard, HBA 300, 600 Full Duplex, Dual Port
SATA 1 1 Copper Onboard, HBA 150, 300, 600 Half Duplex, Single Port
USB 127 5 Copper, Wireless Onboard, Adapter card 0.15, 1.5, 48, 500 Single Port

* Note: the generation 1 FCoE CNAs were rated at 10Gb/s for Ethernet and 4Gb/s for Fibre Channel. These were not widely released and were used primarily for proof of concept. The generation 2 FCoE CNAs run at 10Gb/s for both Ethernet and Fibre Channel.

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. Some interface adapters provide hardware offload to improve performance, managability and/or reliability of the data transmission across the respective interface. The transfer rates listed are across a single port at half duplex.

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.

Beginning with 10GbE and 10GbFC (for ISL’s), some of the newer speeds emerging in 2010 and beyond, a newer “64b/66b” encoding scheme is being used to improve data transfer efficiency. 64b/66b is planned for 16Gb FC and higher data rates for IB. 64b/66b encoding is not directly compatible with 8b/10b, but the technologies that implement it will be built so that they can work with the older encoding scheme.

History

Products became available with the interface speeds listed during these years.

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. Looking at past history shows that several of these interfaces are on a three-to-four year development cycle for the next improvement in speed. It is reasonable to expect that pace to continue.

It should be noted that it typically takes several months after the specification is complete before products are generally available in the marketplace. 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.

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 called a poor signal-to-noise ratio or simply “too noisy”.

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.

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

OM3 and OM4 are newer multi-mode cables that are “laser optimized” (LOMMF) and support 10 Gigabit Ethernet applications. OM3 and OM4 cables are also expected to support 40 Gigabit Ethernet and 100 Gigabit Ethernet applications with operating range of 0.5 to 100m for OM3 and up to 125m for OM4.

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
OS1
 single-mode 9 µm 1310 nm
1550 nm		 — Yellow

Fiber Optic Cable by Distance and Speed
OM1 OM2 OM3 OM4
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 150m * 190m *

* These are conservative estimates of distances supported for OM3 and OM4 cables at 10Gb/s. Specific implementations may support up to 300m for OM3 at 10Gb/s.

Distances supported in actual configurations are less than the distance supported by the raw cable.

Active Copper vs. Passive Copper

Passive copper connections are common with many interfaces. The industry is finding that as the transfer rates increase, passive copper does not provide the distance needed and takes up too much physical space. The industry is moving towards an active copper type of interface for higher speed connections, such as 6Gb/s SAS. Active copper connections include components that boost the signal, reduce the noise and work with smaller-gauge cables, improving signal distance and airflow. These active copper components are expected to be less expensive and consume less electric power than the equivalent components used with fiber-optic cables.

View other technology comparison summaries or our complete list of news and reports.