Microsoft KB Archive/328695

= PRB: Server for NFS is Slower after Upgrading from Services for UNIX Version 2.x to Version 3.0 =

Article ID: 328695

Article Last Modified on 2/2/2004

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APPLIES TO


 * Microsoft Windows Services for UNIX 3.0 Standard Edition

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This article was previously published under Q328695



SYMPTOMS
When you use Server for NFS after you have upgraded from Microsoft Services for UNIX 2.x to 3.0, you may notice slower write times from NFS clients. Specifically, you see slower file copy (file write) times from your NFS clients to the Services for UNIX Server for NFS server. This applies to any NFS client (such as UNIX or Linux) that may be writing data to the Services for UNIX NFS server.

NOTE: This article may also help improve performance if you use only Services for UNIX version 3.0 and you notice slow file write times with Server for NFS (regardless of whether you have upgraded).



CAUSE
In Server for NFS, a configuration setting determines whether the writes are cached or committed; that is, whether the writes are cached and sent to the file system, or are immediately committed upon request from the client.

In Services for UNIX 2.0, the default setting is Caching on.

In Services for UNIX 3.0, the default setting is Caching off. For more information about this important change in caching, see the &quot;More Information&quot; section of this article.

Frequently, NFS caching greatly speeds up NFS file writes, therefore, turning on caching may resolve your file write or general performance issues.



RESOLUTION
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

The registry value that controls this setting is as follows:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NfsSvr\Parameters\UseWriteCache

The default for Caching off is 0. To turn on write caching, set the value to 1.



STATUS
This behavior is by design. The intent is to improve the stability of the Server for NFS product.



IMPORTANT
The default caching setting in Services for UNIX 3.0 was changed to Caching off because NFS clients may incorrectly assume that all the writes were safely committed to stable storage, however, the writes were only in the Server for NFS cache.

Although Server for NFS informs the NFS client that the data has been safely written to disk, the data is still stored in cache, and is waiting to be written to disk. This might cause file corruption issues if, for example, you lose your power supply to the Server for NFS server while data is still in the cache. At this point, the NFS client assumes that data that was lost (in the NFS cache when the Services for UNIX server lost power) was actually safely written to disk.

In version 3.0, the default setting of Caching off means that all the write requests are immediately committed to disk before a response is sent. Although Caching off does frequently slow NFS file writes, it does improve the stability of the product.

WARNING: Turn caching on only if you are willing to risk file corruption if any issue with the Services for UNIX server causes the cache to be lost (for example, if the system shuts down, stops responding, loses its power supply, or experiences other serious issues).

Keywords: kbprb kbdswsfu2003swept KB328695

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