IBM Midrange System DS4000 Series Hardware Manual page 120

EXP5000 and EXP520 ESM board
The ESMs contain the storage expansion enclosure control logic, interface ports, and LEDs.
Each ESM has four SFP module ports that you could use to connect the storage expansion
enclosure to the storage subsystem. However, only the two ESM SFP ports (labeled 1A and
1B) near the center of the storage expansion enclosure are used. The SFP ports labeled 2A
and 2B are reserved for future use. Refer to Figure 3-74.
1A
Figure 3-74 EXP5000 and EXP520 ESM ports
The EXP5000 and EXP520 ESM board allows for host based monitoring and control of the
subsystem through SCSI-3 Enclosure Services (SES) over the FC link.
The EXP5000 and EXP520 supports two ESM CRUs to help provide system redundancy.
Each ESM connects a separate Fibre Channel loop to one of the two Fibre Channel ports on
the disk drives, which is designed to provide both loops access to all drives. It is designed to
maintain access to all drives through the second loop and ESM. In the event of an FC ESM
failure or inoperable loop, access to all drives is still available through the second loop and
ESM.
There are switches inside ESM that allow direct access (1 hop) to a required disk from ESM,
as shown in Figure 3-75.
In
Out
In
Out
Figure 3-75 EXP5000 and EXP520 switched architecture
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IBM Midrange System Storage Hardware Guide
2
4
1B
SFP
SFP
D D D
R R R
I I I
V V V
E E E
SFP
SFP
1A
Switched fabric processor ESM A
FC-SW
D D D D D D
R R R R R R
I I I I I I
V V V V V V
E E E E E E
FC-SW
Switched fabric processor ESM B
ESM B
ID/
Diag
2
4
1B
D D D D D D
R R R R R R
I I I I I I
V V V V V V
E E E E E E
D
R
I
V
E