With the introduction of Windows Server 2025, the page size of the Active Directory database (AD database) was increased from 8 kilobytes (KB) to 32 KB. This significant increase is intended to eliminate numerous limitations that were previously caused by the smaller page size.

However, there is a compatibility pitfall lurking here, especially for environments where migration to Windows Server 2025 is performed using an in-place upgrade. In such cases, the database page size remains at 8 KB by default, which may lead to unexpected conflicts in the future.

The ESE database and the 32 KB option

In its official support article “What’s new in Windows Server 2025,” Microsoft highlights the new features of Active Directory Domain Services (AD DS). The article explains that the Active Directory database is based on the Extensible Storage Engine (ESE), which has been operating with a fixed 8 KB page size since Windows 2000.

In Windows Server 2025, it is now possible to initialize the AD database with the new, larger 32 KB page size.

It is important to note that if this 32 KB option is configured on a domain controller (DC), it must be applied consistently throughout the entire forest (overall structure). However, this setting is not applied during an in-place upgrade. The upgraded server retains the original 8 KB page size.

Confirmation from the community

We became aware of this critical issue through feedback from the community, which warns that an in-place upgrade of DCs can cause additional problems. One reader pointed out that maintaining the 8 KB size during upgrades is a hidden problem, as Microsoft’s change was not made without reason and will eventually have a negative impact.

Microsoft’s recommendation for domain upgrades supports this cautious approach:

The recommended approach to upgrading a domain is to promote new servers running a newer version of Windows Server to domain controllers and demote older domain controllers as needed. This method is preferable to updating the operating system of an existing domain controller, also known as a direct upgrade.

The 32 KB function cannot be activated.

The urgency of this issue was once again brought home to us when we came across a Facebook post that referred to MVP Jorge de Almeida Pinto’s detailed analysis. His blog post (2025-11-14) 32K Pages Size vs 8K Pages Size On W2K25 DCs – That Could Be A Problem! explains why administrators should avoid an in-place upgrade at all costs.

Pinto tested the situation in his laboratory environment and found that:

• • As long as even a single DC remains in the AD forest that uses the old 8 KB page size, the new 32 KB feature cannot be enabled.
  • Affected DCs are those that have either no value (non-2025 DC) or the value 8192 (2025 DC from in-place upgrade) in the AD attribute msDS-JETDBPageSize in the NTDS settings object.
  • These affected domain controllers must either be completely removed from the forest or replaced with newly installed Windows Server 2025 DCs in order to use the 32 KB feature.

Administrators are advised to carefully review Jorge de Almeida Pinto’s detailed description of the test results in order to avoid these complications when migrating to Windows Server 2025.

Read the full article here:

Windows Server 2025: Die Active Directory Page Size-Falle (8k versus 32k)