Chapter 11. Maintaining A Storage Subsystem; Routine Maintenance; Running A Media Scan - IBM System Storage DS3000 Programming Manual

Chapter 11. Maintaining a storage subsystem

Maintenance covers a broad spectrum of activity with the goal of keeping a storage subsystem
operational and available to all hosts. This chapter provides descriptions of commands you can use to
perform storage subsystem maintenance. The commands are organized into four sections:
v Routine maintenance
v Performance tuning
v Troubleshooting and diagnostics
v Recovery operations
The organization is not a rigid approach, and you can use the commands as appropriate for your storage
subsystem. The commands listed in this chapter do not cover the entire subsystem of commands you can
use for maintenance. Other commands, particularly the set commands, can provide diagnostic or
maintenance capabilities.

Routine Maintenance

Routine maintenance involves those tasks that you might perform periodically to make sure that the
storage subsystem is running as well as possible or to detect conditions before they become problems.

Running a Media Scan

Media scan provides a way of detecting disk drive media errors before they are found during a normal
read from or write to the disk drives. Any media scan errors that are detected are reported to the Event
Log. The Event Log provides an early indication of an impending disk drive failure and reduces the
possibility of encountering a media error during host operations. A media scan is performed as a
background operation and scans all data and redundancy information in defined user logical drives.
A media scan runs on all of the logical drives in the storage subsystem that have these conditions:
v Has Optimal status
v Has no modification operations in progress
v Has media scan enabled
Errors that are detected during a scan of a user logical drive are reported to the Major Event Log (MEL)
and handled as follows:
Unrecovered media error – The disk drive could not read the requested data on its first try or on any
v
subsequent retries. The result of this action is that for logical drives with redundancy protection, the
data is reconstructed, rewritten to the disk drive, and verified, and the error is reported to the Event
Log. For logical drives without redundancy protection, the error is not corrected, but it is reported to
the Event Log.
v Recovered media error – The disk drive could not read the requested data on its first attempt. The
result of this action is that the data is rewritten to the disk drive and verified. The error is reported to
the Event Log.
Redundancy mismatches – Redundancy errors are found, and a media error is forced on the block
v
stripe so that it is found when the disk drive is scanned again. If redundancy is repaired, this forced
media error is removed. The result of this action is that the first 10 redundancy mismatches found on a
logical drive are reported to the Event Log.
Unfixable error – The data could not be read, and parity information or redundancy information
v
could not be used to regenerate it. For example, redundancy information cannot be used to reconstruct
data on a degraded logical drive. The result of this action is that the error is reported to the Event Log.
© Copyright IBM Corp. 2008, 2012
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