Lazy Writer, NTFS and Registry flush in Windows 11 25H2

Short answer

These parameters determine when Cache Manager, NTFS and Configuration Manager start writing and release data. They do not change the speed of the disk itself. MaxLazyWritePages, LargeWriteSize, NtfsMemoryUsage and RegistryLazyFlushInterval are read by different parts of the system code and do not replace each other. Increasing the values can reduce the frequency of writes, but more data will accumulate before it happens.

What was tested

We tested which parameters of lazy writing, NTFS memory usage and registry hive writing are read by the system code, how their values are normalized and what increasing the intervals and thresholds changes.

Scope of research

Windows 11 25H2 build 26200.9168, x64; components ntoskrnl.exe and ntfs.sys, system tracing in VMware. Real drives and emergency power-off scenarios were not tested.

Methodology

Analysis of system components, observation of parameter reads in boot and runtime tracing, verification of value normalization and comparison with public Microsoft documentation.

Canonical values

Registry path	Value	Type	Default/normalization	Reader and timing
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management	MaxLazyWritePages	REG_DWORD	256 pages on client Windows	ntoskrnl.exe, early Cache Manager and runtime reload
same path	LargeWriteSize	REG_DWORD	0 — soft throttle disabled	ntoskrnl.exe, Cache Manager
HKLM\SYSTEM\CurrentControlSet\Control\FileSystem	NtfsMemoryUsage	REG_DWORD	system default NTFS	ntfs.sys, driver initialization
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Configuration Manager	RegistryLazyFlushInterval	REG_DWORD	60 seconds	ntoskrnl.exe, Configuration Manager

Lazy Writer: MaxLazyWritePages and LargeWriteSize

MaxLazyWritePages sets the number of pages for the Cache Manager lazy writing mechanism. By default, client Windows 11 25H2 uses 256 pages, the server system type 2048. It can be set explicitly from 1..32768 pages.

LargeWriteSize is set in KB and enables a separate mechanism for soft throttling of large write operations. With the standard value 0, throttling is disabled. The value 64, for example, reduces the lazy write pass from 256 to 64 pages and simultaneously enables throttling of operations of 64 KB and larger. Writes become more frequent and the portions smaller.

The number of pages does not determine the exact size of a single disk operation: Cache Manager takes into account the accumulation of modified pages, the file type and the state of the volume. When the threshold is increased, part of the write is deferred. Too large a threshold can amplify write bursts and increase the amount of not yet saved pages.

Change these parameters only if there is a reproducible problem with lazy writing under a specific workload. For an ordinary system, the default values are the most predictable.

NtfsMemoryUsage

ntfs.sys is read by NtfsMemoryUsage during driver initialization and is taken into account when choosing NTFS memory usage rules. In the research trace, a system process accessed this value.

This parameter does not directly switch the size of the user paged pool. Its effect depends on the NTFS version and the load on the volume.

The parameter should be checked only in a separate drive test with a large number of file operations. A universal benefit for applications has not been proven.

RegistryLazyFlushInterval

Configuration Manager periodically writes modified registry hive data to disk. In the Windows 11 25H2 code, the default interval is 60 seconds. The parameter is measured in seconds: 0x5000 equals 20480 seconds, or approximately 5.7 hours. It is read at the beginning of kernel initialization, so an ordinary boot trace may not contain this event.

With a larger interval, background writing occurs less often, and changes remain only in memory longer. In the event of an emergency power-off, changes over a longer period can be lost. Reducing the interval makes writing more frequent, but does not speed up registry reads.

The parameter affects the reliability of data preservation and the write schedule. Without a measured problem, leave the default value.

What is confirmed

• The read code was found in ntoskrnl.exe, ntfs.sys and Cache Manager mechanisms.
• In the build studied, RegistryLazyFlushInterval defaults to 60 seconds.
• Cache Manager can re-read settings during operation; some kernel parameters are read only at boot.
• The presence of a parameter in the registry does not prove faster disk or application performance.

What is not confirmed

• An increase in disk or application speed from changing the parameters.
• Behavior on RAID, NVMe/SATA and other file systems.
• The consequences of an emergency power-off with a large RegistryLazyFlushInterval.

Practical conclusion

For an ordinary system, leave the default values. Change the parameters only if there is a reproducible problem with lazy writing, and determine in advance the acceptable amount of not yet saved data.

Restoring the state

Return the standard values or delete the optional entries. Some kernel parameters are applied on the next boot, so reboot Windows for a clean comparison.

Limitations

The results apply to Windows 11 25H2 build 26200.9168. Different file systems, RAID, NVMe/SATA controllers and emergency recovery of registry hives after a power-off were not tested.

The research and the tools used belong to the BoosterX developer, so the developer has a direct interest in the results. The methodology and the boundaries of applicability are described above, and the conclusions can be verified against open data and the listed public sources.

Sources

• Cache Manager: system cache architecture, Microsoft Learn, checked 2026-09-01.
• NTFS overview: purpose of NTFS, Microsoft Learn, checked 2026-09-01.

Public sources checked: 2026-09-02.

Change history

• 2026-09-20: added a conflict-of-interest disclaimer.
• 2026-09-02: first publication; the read code, normalization and boundaries of the practical benefit of the parameters were confirmed.