Make sure that your DDB is hosted on the recommended configuration referenced in Deduplication Building Block Guide. If DDB is hosted on the recommended configuration and the QI performance is still slow, then verify and perform the following:
Make sure that there is no anti-virus software running on the DDB MediaAgent.
If DDB backups are scheduled to run very often, make sure to reduce the frequency of the schedule.
If VSS Snap is configured on the same DDB volume, make sure to configure on a different hard disk compared to the DDB volume. This will improve performance of the QI during the DDB backups.
Move Operating System Paging file on the DDB MediaAgent to a faster disk.
For RAID disks, enable Disk Controller caching.
Verify the number of VSS shadows on the DDB volume by running the following command:
vssadmin list shadows /For= DDB VolumeDDB Volume - is the actual volume drive letter (for example D:) where the DDB is configured.
If there are no DDB backup jobs running and you do not have any third party software's installed on the DDB MediaAgent that is creating and using shadows, delete any existing VSS shadows on the DDB volume by using the following command:
vssadmin delete shadows /For= DDB Volume