IBM Midrange System DS4000 Series Hardware Manual page 448

Figure 7-67 shows both the physical and logical views in Storage Manager when a disk fails in
a redundant array. There is a clock symbol next to one of the logical drives associated with
the degraded array indicating that reconstruction is in progress on that logical drive. A
progress bar is displayed when the logical drive is selected.
Figure 7-67 Storage Manager view after disk failure
At this point, we have a choice:
The simplest and most common solution is to physically replace the failed disk. This
results in an automatic copyback operation from the hotspare onto the new drive. When
complete, the hotspare returns to an unassigned hotspare role.
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3. Hotspare takes over
2. Array degraded
1. Disk fails