User`s guide

264 Implementing an Open IBM SAN
The motivation to use cascaded directors is not limited to increased port counts.
Cascaded directors can be used to create a SAN that spans large distances.
Unique to INRANGE Directors, ports used for Inter Switch Links are called
T_Ports (Trunk ports). Every director port can be used for T_Port operation. No
manual setting is needed since ISL connections are automatically detected and
the affected ports are set to T_Port.
ISLs can be run on either ShortWave GBICs or LongWave GBICs. The usage of
LongWave GBICs enables the creation of long distance fabrics. The actual
supported distance between INRANGE directors can be further expanded by
using channel extenders or multiplexers.
Figure 3-77 shows an example where cascaded directors are used to allow host
based mirroring over long distances:
Figure 3-77 One INRANGE fabric consisting of two cascaded directors
Cascading is a very effective and easy to use method to extend distances and
increase maximum port count. However we need to consider some of the
implications which are:
򐂰 By connecting multiple directors they will become one fabric inheriting all the
rules for one fabric, including:
– Name server zones are valid fabric-wide.
– Numbers and names of name server zones must be unique fabric-wide.
– Either all or none of the director ports in a fabric are hard zoned.
Two LongWave connections
used as InterSwitchLink (ISL)
Onefabricmadeup
of two cascaded directors