The Index Fragmentation alarm is raised when the largest Index file on the SQL Server is more than 5% fragmented. It is a good idea to defragment large index files that are more than 5% fragmented.
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When the alarm is raised:

  1. Open SQL Server | Databases drilldown | Fragmented Indexes.
  2. Select the index to defragment and click Fragmented Indexes | Generate defragmentation script.
  3. Use SQL Server Management Studio to schedule a job to run this script during a quiet period.