Slowness in Windows Explorer when you click a subfolder or drive on a remote server

Applies to: Windows Vista BusinessWindows Vista Business 64-bit EditionWindows Vista Home Basic

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

Symptoms


Symptom 1
When you click a subfolder or drive on a remote server over a slow link, you may see an hourglass or a green navigation progress bar for a long time. The delay affects not only Windows Explorer but also any new SMB file request from the client to the same remote file server.
Symptom 2
If you are using Server Message Block (SMB) version 2 (SMBv2) or a later version and are performing a file copy to a share over a slow network, the Explorer window in which the file copy is occurring becomes unresponsive for 30 seconds to 2 minutes.

Cause


The slowness occurs because the client is already copying a file to the remote server. File transfer algorithms were updated in Windows Vista and later versions to achieve faster file transfers. The newer versions of Windows can copy files more than two times as fast over a Local Area Connection (LAN) connection.

Windows Vista and later versions checks whether the underlying stream is SMB version 1 (SMBv1) or a later version. If the stream is SMBv1, the operating system still uses 32-kilobyte (KB) chunks. But if the stream is SMBv2 or a later version, the operating system uses a chunk size of 1 megabyte (MB). This causes Explorer to be unresponsive for slow networks because it can respond to user messages only after 1 MB is copied.

Resolution


To resolve this issue, use a different mechanism to upload or download large files over a slow link. For example, use a mechanism that does not use SMB. Instead use a transfer protocol such as FTP or HTTP.
Important Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration  in case problems occur.

To work around this issue, configure the client by using the following registry entries to achieve behavior that resembles Windows XP behavior. File transfer times over slow links are only slightly increased when you use these registry entries, and the client seems to be much more responsive:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\System
"CopyFileBufferedSynchronousIo"=dword:00000000
"CopyFileChunkSize"=dword:00010000
Note Adding these registry entries can cause SMB file copies to take more than two times as long over a fast LAN connection. You should add these registry entries only when they are needed.