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Volume Defragment Error Handling

Overview

This document applies to Volume Defragment for NetWare, version 1.28 and later versions.

Volume Defragment for NetWare is designed to detect and in some cases support NetWare volumes that have problems. Some types of problems will prevent defragmentation of volumes from starting.

There are several problems that a NetWare volume can have:

  • Configuration Errors.
  • Structural Errors.
  • Hardware Errors.

Configuration Errors:

Configuration errors are problems with missing volume segments, segments that are not properly configured, missing mirror partitions, etc.

Before a volume defragment begins, the configuration of the volume and its NetWare partitions are verified for correct configuration. If any problems are found during this analysis, the volume will not be defragmented.

For Mirrored Partitions, all mirrors must be present and be 100% mirrored.

Structural Errors:

Structural errors are problems with the volume data structures such as FAT Tables, Directory Tables, etc.

A very comprehensive "Volume Check" is performed on a volume before a defragment begins. If any problems are found, the volume will not be defragmented.

Structural errors are not corrected by the software. If errors are found, run VREPAIR to correct the errors.

Hardware Errors:

Hardware errors include Media Errors, Corrected Media Errors and other hardware problems with the disk drive and controllers.

Most hardware problems are detected during the configuration tests. Media errors are detected during a volume defragment.

Media errors during a volume defragment will not cause a volume defragment to fail. If a Media Error happens during the read of a volume block, the data will not be moved. If a Media Error happens during the write of a volume block, the data will not be moved.

An exception to the above rule: If a volume is mirrored, and a read error occurs, a read attempt will be made to one of the other mirrors. If the read succeeds, the volume block will be moved and the old location will be marked bad.

Logging of errors:

There is a command line option "-logfile=filename" that creates a file on either a NetWare volume or DOS partition. Errors, warnings and status information will be written to the file during a volume defragment.

During a defragment, the status screen displays the total number of volume blocks that could not be moved due to sector read / write errors in the field: "Blocks Not Moved". For normal healthy volumes, this field will be zero at the end of a volume defragment. If this field is greater than zero, then the volume has defective data areas that have not been corrected by NetWare's Hotfix strategy.

Volume with defective data areas will often report errors on the console during normal server operation (not during a volume defragment):

4-20-2001 9:26:56 am: FILESYS-5.10-178 [nmID=60017]
Error reading file NWDIR.JAR.
Offset 000315AEh data stream 0.
Read was requested by user ADMIN on station 6.
File path SYS:JAVA\BEANS\NWDIR.JAR.

This error message means that a user attempted to read data from this file. The disk read returned "Media Error" and the read could not be completed. For some reason NetWare does not Hotfix this data block. We recommend backing up this volume, replacing the disk drive and then doing a volume restore.

Read more about this error in our Novell NetWare File System  Errors document or our May newsletter.

NetWare Hotfix sectors:

Volume Defragment for NetWare supports NetWare Hotfix sectors. This support was added to version 1.28. Previous version prevented defragmentation of volumes with Hotfix sectors.

Disk read errors during volume defragment.

If a sector read error occurs during a block move, and the volume is not mirrored, the block is not moved and is left in its current location.

If the volume is mirrored, the read will be attempted on the other mirror drives. If the read succeeds, the block move will complete.

Disk write errors during volume defragment.

If a sector write error occurs during a block relocation, the block is not moved. Sector writes only occur when writing a volume block to a free location on the volume. Internally the software keeps track of this bad location and does not use this volume block for any further block moves.

Summary.

Volume Defragment for NetWare handles disk errors very gracefully. For most error types the solution is to not defragment the current file. A defragment involves moving data blocks from used locations to free locations - an error just means abort the current block move.

       
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Last modified: Tuesday March 14, 2006.