IBM Midrange System DS4000 Series Hardware Manual page 425

Figure 7-57 illustrates the drive-side connections for one redundant channel pair in a 16
enclosure configuration. On the DS5300, each drive channel is associated with two ports.
There are four drive channels and eight associated ports per controller. One channel from
each controller combines to form a
Chan
1
DS5300
Chan
2
Controller
Chan
A
3
Chan
4
Figure 7-57 Drive-side connections
Degraded drive channel
The controller automatically fails a disk or ESM whenever an error threshold is exceeded.
However, if there are excessive errors detected on a drive channel, then the controller will
mark the channel as
routed via the alternate channel in the redundant channel pair until the problem is identified
and resolved. This is where we need to use available tools to determine which storage
subsystem (enclosure) or component (cable, SFP, or ESM) on the channel is causing the
excessive errors.
The main tools for diagnosing drive-side problems include:
View Connections
Storage Subsystem Profile
Major Event Log (MEL)
Read Link Status Diagnostics
SOC Statistics
Capture State Information
ESM A ESM B
8
1B 1A 1A 1B
7
6
5
4
3
2
1
1B 1A 1A 1B
ESM A ESM B
degraded
. In this state, the channel is still available, but all I/Os are
Chapter 7. Advanced maintenance, troubleshooting, and diagnostics
redundant drive channel pair
ESM A ESM B
1B 1A 1A 1B
1B 1A 1A 1B
ESM A ESM B
.
1 Chan
2
5
DS5300
3
Chan
4
6
Controller
Chan
5
B
7
6
7
Chan
8
8
407