SAN Solution Installation Guide

Installation
Hubs
Chapter 22-8
Hubs
Hubs may be installed between the switch and the library, but are NOT
supported between servers and switches or between two switches (i.e.,
switch spanning). (See Figures 2-1 through 2-4 on pages 2-9, 2-10, 2-11,
and 2-12.)
CAUTION To prevent damage to the fiber-optic cable, DO NOT have a bend radius
of less than three inches. Keep all sharp objects away from the cable and
place the cable where it will not be crushed by nearby equipment.
FC hubs may not be used in place of switches for providing shared access
to tapes and tape libraries. Loop topologies allow for one host to interrupt
the backup taking place from another host to a tape device. FC switches
isolate host interactions from each other, providing a more robust
environment for streaming data.
Hubs may be used with switches to aggregate tape drive connections into
a switch. However, they may not be used between hosts and switches.
Also, multiple hubs may not be cascaded when used to aggregate tape
drive connections to a switch port.
When aggregating tape drives, no more than 10 DLT 8000 drives would
be configured per hub. This assures there is not a performance
bottleneck between the tape drives and switch.