User's Manual

I/O modules
TwoI/Omodulesprovideaninterfacebetweenthedisksandthehostsystem.TheI/Omodulesareused
to route data to and from the disks in a dual-loop configuration to eliminate a single point of failure.
Each disk drive is connected to both I/O module A and I/O module B (Figure 4-3). Each I/O module is
connected to an independent, external FC loop. I/O module A connects to loop A, and I/O module B
connects to
loop B (see Figure 1 on page 14).
CAUTION:
Keep the loops completely separate to ensure that the failure of a single component (I/O module,
transceiver, or cable) does not stop data transmissions to active drives.
25175a
1 2 3 4 5
1. FC loop B
4. I/O module A
2. I/O module B
5. FC loop A
3. FC disks (3 are shown, but up to 14 disks are supported in each DS2500)
Figure 4 Redundant disk connections
The operation and function of both I/O modules are identical. Each I/O module has two ports that
can transmit and receive data for bidirectional operation. Port use and connections are configuration
dependent (see "Cables and cabling" on page 24). Each port is identified with a transceiver element
number,anditsstatusisdisplayedonanLED(Figure 5). Port 1 is the bottom loop port, and port
2isthetoploopport.
• Port 2 LED—On indicates that a signal was detected at the top transceiver.
• Power LED—On indicates that power is present on the I/O module.
• Port 1 LED—On indicates that a signal was detected at the bottom transceiver.
2500 Disk System user guide
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