channel with EXP810s (4) operates at 4 Gbps, while at the same time the
other redundant drive channel with EXP710s (5) operates at 2 Gbps. This
is possible because all 4 Gbps EXP810s (2) are connected behind a
given redundant drive channel pair, and all 2 Gbps EXP710s (3) are
connected to a different redundant drive channel pair.
Host channels
Each DS4800 controller has four single-ported host fibre channel ports. The
controllers perform link speed negotiation on each host channel fibre
channel port (also referred to as auto-negotiation). Each host channel can
operate at either 1, 2, or 4 Gbps fibre channel speeds. The controllers
interact with the fibre channel host bus adapter ports in the host server or
the fibre channel switch to determine the fastest compatible speed between
the controllers and the host or switch. The fastest compatible speed
becomes the operating speed of the link. If the host or switch on the other
end of the link are either fixed-speed or not capable of negotiating, the
controllers automatically detect the operating speed of the other host or
switch and set the controller link speed accordingly. Link speed negotiation
for a given host channel is limited to link speeds supported by the small
form-factor pluggable (SFP) module on that channel.
The controllers will enter into auto-negotiation at these points in time:
v Start-of-day
v Detection of a link-up event after a previous link-down event
58
85
Controller A
Controller B
2
3
1
4
5
ds48060
Figure 5. DS4800 configuration with 2 Gbps and 4 Gbps enclosures in different drive channel pairs
Chapter 1. Introduction 13
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