Chapter 1. Disk attachment technology 5
Optical SFP modules are commonly available in several categories:
850 nm 550m MMF (SX)
1310 nm 10 km SMF (LX)
1550 nm [40 km (XD)]
80 km (ZX)
120 km (EX or EZX)
SFP transceivers are also available with a copper cable interface, allowing a host device
designed primarily for optical fiber communications to also communicate over unshielded
twisted pair networking cable.
SFP transceivers are commercially available with capability for data rates up to 4.25 Gbit/s.
The standard is expanding to SFP+ which supports data rates up to 10.0 Gbit/s (that will
include the data rates for 8 gigabit Fibre Channel, 10 GbE, and OTU2).
FC World Wide Names (WWN)
A World Wide Name (WWN) or World Wide Identifier (WWID) is a unique identifier that
identifies a particular Fibre Channel, Advanced Technology Attachment (ATA) or Serial
Attached SCSI (SAS) target. Each WWN is an 8 byte number derived from an IEEE OUI and
There are two formats of WWN defined by the IEEE:
Original format: addresses are assigned to manufacturers by the IEEE standards
committee, and are built into the device at build time, similar to an Ethernet MAC address.
The first 2 bytes are either hex 10:00 or 2x:xx (where the x's are vendor-specified),
followed by the 3-byte vendor identifier and 3 bytes for a vendor-specified serial number
New addressing schema: first nibble is either hex 5 or 6 followed by a 3-byte vendor
identifier and 36 bits for a vendor-specified serial number
1.2 Serial Attached SCSI (SAS) disk attachment
SAS is a computer bus used to move data to and from computer storage devices such as
hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the
parallel SCSI bus technology, and uses the standard SCSI command set.
At the time of writing, typical SAS throughput is 6 Gbps full duplex. SAS has the capability to
reach 24 Gbps if the host can drive it at that speed. When the first 6 Gbps connection is full,
the next 6 Gbps connection is used, and so on, up to four connections.
Figure 1-3 on page 6 shows the SAS technical specifications.