Certain services and tasks in Windows 7, Windows 8/8.1, and Windows 10 can cause the OS disk of an instant clone or a View Composer linked clone to grow incrementally, even when the machine is idle. If you disable these services and tasks, you can control the OS disk growth.

Services that affect OS disk growth also generate I/O operations. You can evaluate the benefits of disabling these services for full clones as well.

Before you disable the Windows services that are shown in Table 1, verify that you took the optimization steps in Optimize Guest Operating System Performance.

Table 1. Impact of Windows Services and Tasks on OS Disk Growth and IOPS
Service or Task Description Default Occurrence or Startup Impact on OS Disk Impact on IOPS Turn Off This Service or Task?
Windows Hibernation Provides a power- saving state by storing open documents and programs in a file before the computer is powered off. The file is reloaded into memory when the computer is restarted, restoring the state when the hibernation was invoked. Default power-plan settings disable hibernation. High.

By default, the size of the hibernation file, hiberfil.sys, is the same as the installed RAM on the virtual machine. This feature affects all guest operating systems.

High.

When hibernation is triggered, the system writes a hiberfil.sys file the size of the installed RAM.

Yes

Hibernation provides no benefit in a virtual environment.

For instructions, see Disable Windows Hibernation in the Parent Virtual Machine.

Windows Scheduled Disk Defragmentation Disk defragmentation is scheduled as a background process. Once a week High.

Repeated defragmentation operations can increase the size of the OS disk by several GB and do little to make disk access more efficient .

High Yes
Windows Update Service Detects, downloads, and installs updates for Windows and other programs. Automatic startup Medium to high.

Causes frequent writes to the OS disk because update checks occur often. The impact depends on the updates that are downloaded.

Medium to high Yes, for instant clones, and for View Composer linked clones that you refresh or recompose regularly.
Windows Diagnostic Policy Service Detects, troubleshoots, and resolves problems in Windows components. If you stop this service, diagnostics no longer function. Automatic startup Medium to high.

The service is triggered on demand. The write frequency varies, depending on demand.

Small to medium Yes, if you do not need the diagnostic tools to function on the desktops.
Prefetch/Superfetch Stores specific information about applications that you run to help them start faster. Always on, unless it is disabled. Medium

Causes periodic updates to its layout and database information and individual prefetch files, which are generated on demand.

Medium Yes, if application startup times are acceptable after you disable this feature.
Windows Registry Backup (RegIdleBackup) Automatically backs up the Windows registry when the system is idle. Every 10 days at 12:00 am Medium.

Each time this task runs, it generates registry backup files.

Medium. Yes. Both instant clones and View Composer linked clones let you revert to a snapshot and achieve the goal of restoring the registry.
System Restore Reverts the Windows system to a previous, healthy state. When Windows starts up and once a day thereafter. Small to medium.

Captures a system restore point whenever the system detects that it is needed.

No major impact. Yes. Both instant clones and View Composer linked clones let you revert to a healthy state.
Windows Defender Provides anti-spyware features. When Windows starts up. Performs a quick scan once a day. Checks for updates before each scan. Medium to high.

Performs definition updates, scheduled scans, and scans that are started on demand.

Medium to high. Yes, if other anti-spyware software is installed.
Microsoft Feeds Synchronization task (msfeedssync.exe) Periodically updates RSS feeds in Windows Internet Explorer Web browsers. This task updates RSS feeds that have automatic RSS feeds synchronization turned on. The process appears in Windows Task Manager only when Internet Explorer is running. Once a day. Medium.

Affects OS-disk growth if persistent disks are not configured. If persistent disks are configured, the impact is diverted to the persistent disks.

Medium Yes, if your users do not require automatic RSS feed updates on their desktops.