LAN Manager Heuristics and Windows NT Registry Entries

The information in this article applies to:

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Workstation version 4.0

SUMMARY

Several of the wrkheuristic and srvheuristic values in the Microsoft LAN Manager LANMAN.INI file directly correspond to Registry entry values on a Microsoft Windows NT or Microsoft Windows NT Advanced Server machine. Some of those values are described below.

WORKSTATION HEURISTICS

The following LAN Manager workstation heuristics map to Windows NT workstation parameters in the Registry at HKEY_LOCAL_MACHINE\System\ CurrentControlSet\Services\LanmanWorkstation\Parameters:

WRKHEURISTIC: 0 UseOpportunisticLocking

Indicates whether the redirector should use opportunistic-locking performance enhancement. This parameter should be disabled only to isolate problems.

   Default: 1 (True)

Indicates whether the redirector will complete an unlock operation before it has received confirmation from the server that the unlock operation has completed. Disable this parameter only to isolate problems or to guarantee that all unlock operations complete on the server before completing the application's unlock request.

   Default: 1 (true)

Indicates whether the redirector should buffer character-mode named pipes. Disable this parameter to guarantee that all pipe write operations are flushed to the server immediately and to disable read ahead on character-mode named pipes.

   Default: 1 (True)

Indicates whether the redirector will use the lock-and-read and write-and-unlock performance enhancements.

When this value is enabled, it generally provides a significant performance benefit. However, database applications that lock a range and don't allow data within that range to be read will suffer performance degradation unless this parameter is disabled.

   Default: 1 (True)

Enables the raw-read and write optimization. This provides a significant performance enhancement on a local area network.

   Default: 1 (True)

Specifies whether the redirector should only send a maximum of 512 bytes in a request to an MS-Net server regardless of the servers- negotiated buffer size. If this parameter is disabled, request transfers from the Windows NT redirector could cause the MS-Net server to crash.

   Default: 0 (False)

Specifies whether the redirector should cache files that are opened with only FILE_SHARE_READ sharing access. Usually, if a file is opened with FILE_SHARE_READ specified, the file cannot be buffered because other processes may also be reading that file. This optimization allows the redirector to buffer such files. This optimization is safe because no process can write to the file. Disable this parameter if it is necessary to preserve the strict semantics of the sharing modes specified.

   Default: 1 (true)

Specifies whether the redirector should cache files that are read- only. Usually, if a read-only file is opened, the file cannot be buffered because other processes may also be reading that file. This optimization allows the redirector to buffer such files. This optimization is safe because no process can write to the file. However, another user can modify the file to enable writing to the file, causing loss of data. Disable this parameter if it is necessary to preserve the strict semantics of the sharing modes specified.

   Default: 1 (true)

SERVER HEURISTICS

The following LAN Manager server heuristics map to Windows NT Registry entries at HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\ LanmanServer\Parameters:

SRVHEURISTIC: 5 EnableFCOpens

Specifies whether MS-DOS file control blocks (FCBs) are folded together so that multiple remote opens are performed as a single open on the server. This saves resources on the server.

   Range: Boolean
   Default: 1 (True)

Specifies the priority of all server threads in relation to the base priority of the process. Higher priority can give better server performance at the cost of local responsiveness. Lower priority balances server needs with the needs of other processes on the system.

   Range: 5-50 secs (LAN Manager); 0-15 secs (Windows NT)
   Default: 5 secs (LAN Manager); 5 secs (Windows NT)

Specifies the time that the scavenger remains idle before waking up to service requests. A smaller value for this parameter improves the response of the server to various events, but costs CPU cycles.

   Range: 5-50 secs (LAN Manager); 1-300 secs (Windows NT)
   Default: 5 secs (LAN Manager); 30 secs (Windows NT)

Specifies whether the server maps it to a normal open request with shared-read access when the server receives a compatibility open request with read access. Mapping such requests allows several MS-DOS computers to open a single file for read access.

   Range: 0, 1, 2, 3(LAN Manager); 0 (False), 1 (True) (Windows NT)
   Default: 2 (LAN Manager); 1 (Windows NT)

Specifies the time that the server waits for a client to respond to an oplock break request. Smaller values can allow detection of crashed clients more quickly, but can potentially cause loss of cached data.

   Range: 35-640 secs (LAN Manager); 10-180 secs (Windows NT)
   Default: 35 secs (LAN Manager); 35 secs (Windows NT)

REFERENCES

Documentation from MS LAN Manager Upgrade to Windows NT Advanced Server LAN Manager documentation