How to adjust the RID Block Size

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By default, an RID master provides RID pools containing 500 RIDs to domain controllers within the same Active Directory domain. While there are no reasons to decrease the number of RIDs within a pool and Microsoft recommends to keep the default configuration, you may have exceptional cases where you need to increase this number.

In case you need to adjust the RID Block Size, you can proceed as the following:

  • Identify your RID master using netdom query fsmo
  • Connect to your RID master and update the registry entry RID Block Size which is under the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\RID Values\ with the needed value

The change will be effective when new RID pools are issued to your domain controllers.

The system creates this registry key automatically and its initial value is 0. With this value, the default of 500 is used. Setting this value to less than 500 has no effect, and the default setting is still used. No maximum block size is enforced. However, a value that is too large has an adverse effect on the longevity of the domain.

Also, take note that, in case you have to change this value, it is advised to do it on all your domain controllers so that anyone of them will enforce the same size in case an RID master role transfer or resizing happens.