You must also consider the bandwidth consequences of a complete fabric outage. Although a  complete fabric outage is a fairly rare event, insufficient bandwidth can turn a single-SAN  outage into a total access loss event. Take the bandwidth of the links into account. It is common to have ISLs run faster than host  ports, which reduces the number of required ISLs. To implement remote mirroring over a distance by using the Fibre Channel, you have the  following choices: Of these options, the optical distance extension is the preferred method. IP distance  extension introduces more complexity, is less reliable, and has performance limitations.  However, optical distance extension can be impractical in many cases because of cost or  unavailability. Check the list of supported SAN routers and FC extenders on the online documentation at: IBM FlashSystem 9100 family . Optical multiplexors can extend a SAN up to hundreds of kilometers (or miles) at high speeds.  For this reason, they are the preferred method for long-distance expansion. If you use  multiplexor-based distance extension, closely monitor your physical link error counts in your  switches. Optical communication devices are high-precision units. When they shift out of  calibration, you will start to see errors in your frames. Long-distance optical transceivers have the advantage of extreme simplicity. You do not need  any expensive equipment, and you have only a few configuration steps to perform. However,  ensure that you only use transceivers that are designed for your particular SAN switch. Fibre Channel over IP (FCIP) is by far the most common and least expensive form of distance  extension. It is also complicated to configure. Relatively subtle errors can have severe  performance implications. With IP-based distance extension, you must dedicate bandwidth to your FCIP traffic if the link  is shared with other IP traffic. Do not assume that because the link between two sites has low  traffic or is used only for email, this type of traffic is always the case. FC is far more sensitive  to congestion than most IP applications.  Also, when you are communicating with the networking architects for your organization, make  sure to distinguish between  megabytes per second  as opposed to  megabits per second.  In the  storage world, bandwidth often is specified in megabytes per second (MBps), and network  engineers specify bandwidth in megabits per second (Mbps).  Distance extensions options Optical multiplexors Long-distance SFPs and XFPs Fibre Channel over IP  GLYPH<SM590000> Optical multiplexors, such as dense wavelength division multiplexing (DWDM) or coarse  wavelength division multiplexing (CWDM) devices GLYPH<SM590000> Long-distance Small Form-factor Pluggable (SFP) transceivers and XFPs GLYPH<SM590000> Fibre Channel-to-IP conversion boxes Chapter 6. Copy services  185