Change Pre-Read Redundancy Check - IBM System Storage DS3500 Introduction And Implementation Manual

7914Admin_Logical.fm
The Change Media Scan Settings window has two sections. In the first, you can suspend
media scan or set the scan duration for entire storage subsystem, and in the second, you can
enable or disable scanning for selected logical drives. You can decide if it will be done with or
without the redundancy check.
Suspend media scan
To disable the media scan, select the Suspend media scan check box and click OK. All
media scan functions will be disabled for all logical drives.
Edit scan duration days
To edit the scan duration, make sure Suspend media scan is unchecked and select the new
value in the Scan duration box. Click OK to save the changes.
Logical drive settings
If the media scan is active, you can enable a redundancy check for individual logical drives:
1. Highlight (with help of Ctrl or Shift keys) one or more logical drives you want to set.
2. To enable the media scan, select the Scan selected logical drives check box, choose
with or without redundancy check, and click OK.
3. The changes will be saved on the storage subsystem, and you are informed when it is
completed.

9.5.4 Change Pre-Read Redundancy Check

You can use this option to define the capability of the DS3500 Storage Subsystem firmware to
pre-read logical drive redundancy information and determine if the data of a given logical
drive is consistent (redundant). This check is done on each read operation on the selected
logical drive.
A logical drive that has this feature enabled returns read errors if the data is determined to be
inconsistent by the controller firmware. It happens, for example, if data from one disk of a
RAID 10 array is readable and mirrored data from a second disk is not readable.
Remember that:
You cannot enable this feature for logical drives that do not contain redundancy
information.
You cannot enable this check for high-level logical drives (FlashCopy or Remote Mirror
target logical drives).
You can enable pre-read redundancy check on each logical drive separately.
You can enable this check for normal logical drives, and also on FlashCopy base logical
drives, VolumeCopy source and target drives, FlashCopy repository drives, and Remote
Mirror source drive.
If a logical drive that is configured with a pre-read check is migrated to a RAID 0 type that
does not maintain redundancy information, the metadata of the logical drive continues to
reflect this setting. The read operations from that logical drive ignores pre-read redundancy
check. If the logical drive is subsequently migrated back to a RAID type that supports
redundancy, the feature will become active again.
A similar function is provided if the background media scan is set with a redundancy check.
The Pre-Read Redundancy Check is similar to the Media Scan setting with redundancy check
enabled (see 9.5.3, "Change Media Scan Settings" on page 250). The main difference is that
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IBM System Storage DS3500: Introduction and Implementation Guide
Draft Document for Review March 28, 2011 12:24 pm