IBM Midrange System DS4000 Series Hardware Manual page 422

To modify the Media Scan settings, you need to be in the logical view in the Storage Manager
Subsystem Management window. Then either right-click a logical drive or select Logical
Drive  Change  Media Scan Settings to bring up the Change Media Scan Settings
window shown in Figure 7-56.
Figure 7-56 Media Scan settings
The options displayed at the top, Suspend media scan and Scan duration (days), are global
settings. The logical drive settings at the bottom of the window apply to individual logical
drives, although there is an option to set all logical drives identically by clicking the Select All
button.
To specify the duration (in days) of the media scan, select a number in the Scan duration
(days) box. The media scan duration specifies the number of days over which the media scan
can run on the eligible logical drives. The controller uses the duration period, with its
knowledge of which logical drives must be scanned, to determine a constant rate at which to
perform media scan activities. This rate is maintained regardless of host I/O activity. Choosing
a higher value for the duration will result in the media scan running for a longer period as a
lower priority task.
A redundancy check scans the blocks in a RAID 3, 5, or 6 logical drive and checks the
redundancy information for each block. A redundancy check compares data blocks on RAID 1
mirrored disk drives. RAID 0 logical drives have no data redundancy. There might be a
performance impact when redundancy check is enabled.
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IBM Midrange System Storage Hardware Guide