DIGITAL TCP/IP Services for OpenVMS
Management

The file SYS$STARTUP:UCX$NFS_SERVER_STARTUP.COM also defines a set of logical names that set the file system parameters. Table 14-3 documents these logical names.

Table 14-3 File System Logical Names

Logical Name	Description
UCX$CFS_CACHE_LOW_LIMIT	Defines the minimum size of the free buffer list. Below this number, the file system starts to reclaim used buffers. Default: 4 buffers. The free buffer list needs at least four free buffers (not taken by cache). If the actual number of free buffers is less than UCX$CFS_CACHE_LOW_LIMIT, the used buffers are freed up and returned to the free list, until the size of the free list reaches UCX$CFS_CACHE_HIGH_LIMIT.
UCX$CFS_CACHE_HIGH_LIMIT	Defines the number of buffers the file system tries to keep in the free buffer list. Default: eight buffers. See UCX$CFS_CACHE_LOW_LIMIT. In a busy server environment, setting this parameter higher is likely to improve performance.
UCX$CFS_TRANSFERSIZE	Defines the size, in bytes, of the data transferred between server and client on READ and WRITE operations. Default: 8 Kbytes (8192 bytes). This value is used in most NFS server implementations.
UCX$CFS_KEEP_ALLOC	Defines whether the KEEP_ALLOC option should be turned on or off. Default: 0 (OFF). If the KEEP_ALLOC option is OFF, unused blocks at the end of a file are freed. If it is ON, then unused blocks are kept allocated.
UCX$CFS_SHOW_VERSION	Sets the SHOW_VERSION logical name on or off. If ON, the NFS server returns to the client file names with version numbers, even if there is only one version of the file. Default: 0 (OFF).
UCX$CFS_MODUS_OPERANDI	Defines various operating modes. Use only under the advice of your DIGITAL support representative.
UCX$CFS_FATAL_MESSAGES	Defines the terminal device to which the important error messages are directed, in addition to the normal error messages that are sent to the operator's console. Default: _OPA0:.

14.13 Improving Server Performance

This section provides information to help you identify and resolve problems and tune system performance.

14.13.1 Displaying Performance Information

The SHOW NFS_SERVER command displays information about the running NFS server that you can use to tune its performance. You can issue SHOW NFS_SERVER for a specific client or host if it is listed in the proxy database. The counter information can be especially useful in determining the load on your system.

In the following sample display, the numbers are keyed to the discussion that follows.

UCX> SHOW NFS_SERVER
 
Server:NFS$SERVER                                Loaded: 14-NOV-1995 15:35:01.73 
Status:     ACTIVE                               Running:          0 00:24:21.26 
 
Memory allocated (1)  470260  RPC errors (2)
Message processing:                 Authentication                        0 
  Threads busy (3)         0  Others                                0 
  Threads free                  15  Mount data base: (4)
  Max. threads busy              5    Mounted file systems                1 
  Duplicate cache  xid (5) 0    Current users                       1 
  Duplicate active xid           0    Maximum mounted                     1 
  Dropped                        0    Maximum users                       1 
Data exchange: (6)            NFS operations: (7)
  Bytes sent              11839124    null               0  getattr      42 
  Bytes rcvd              10900824    setattr           12  lookup      186 
  Messages sent               2956    readlink           0  rename        0 
  Messages rcvd               2956    read            1417  write      1284 
  Max. message sent           8292    statfs             1  create        2 
  Max. message rcvd           8328    remove             1  link          0 
Open files: (8)                 symlink            0  mkdir         1 
  Maximum opened                 2    rmdir              1  readdir       7 
  Closed per interval            0  Total NFS operations               2954 
  Currently opened               0  Error messages (9)              0 

1. The amount of memory that the NFS server is using when the command was issued. This amount is affected by the number of threads, size of the volatile user database, mounted file system structures, and the number of opened files.
2. The RPC errors logged for the following: authentication (potential intruder attempts), garbled RPC messages, wrong RPC protocol number, no procedure, no program, and version mismatch. The error logging file contains the information about the hosts and users that caused the erroneous RPC message.
3. The multithreading counters show the number of threads being processed at a given time. The number of threads includes the threads queued to the internet driver for receiving messages and the maximum number of threads that have been simultaneously active in process.
   The value of the multithreading counters equals the specified value of the threads in the NFS startup file. This value indicates that the load on the server is too high for the specified maximum number of threads.
   Increasing the maximum number of threads might improve NFS performance.
4. The mount database counters display the number of mounted file systems and clients currently active within the NFS server. Because of the stateless nature of the server, these counters can contain an inaccurate value.
5. The duplicate/dropped message counter displays the number of duplicate transaction identifiers (XIDs) and dropped messages. The XID counter includes the duplicate XIDs present during message processing and caching, and the number of messages dropped because of busy resources within the OpenVMS environment. A large value indicates that the NFS performance is not good enough to avoid client timeout and message retransmissions. You may want to increase the number of threads to improve NFS performance. You can also reduce the client's retransmission rate by specifying a timeo option when the client mounts the file system.
6. The data exchange counter shows the number of bytes transmitted and received by the NFS server. This value provides an indication of the amount of load on the server.
7. The operation statistics counter displays the number of NFS operations for each operation type.
8. The open file counters display the maximum number of simultaneously open files, currently open files, and closed operations. A high number of files closed per activity time interval means that the clients have simultaneously accessed a large number of files. Accessing a large number of files may affect NFS server performance because of many file open and close operations. You may want to increase the inactivity timer value to improve NFS performance.
   The value of the maximum simultaneously opened files indicates the best value for an open channel quota.
9. The error message counter displays the number of error messages in the error log.

The SHOW CFS command is useful for monitoring the distribution of the file system services and the consumption of system time by the various system services. See the DIGITAL TCP/IP Services for OpenVMS Management Command Reference manual for a detailed description of the SHOW CFS command.

Example 14-1 provides an example SHOW CFS display. The numbers in the example are keyed to the discussion that follows. (The NFS server must be running when you issue this command.)

Example 14-1 SHOW CFS

UCX> SHOW CFS
 
                           CFS SERVICES             13-MAR-1997 14:10:02.74 
   CFS Services(1)               VAX/OpenVMS System Services(2)
-----------------------    ------------------------------------------------ 
CLOSE                 8   
CREATE_FH             1    $ASSIGN            9   $QIO                    0 
CREDIR_FH             0    $DASSGN            8        Access             7 
FREEBUFF              0                                Create             1 
GETATTR              28    $DEQ             182        Deaccess           8 
LINK_FH               0    $ENQ             603                          
LOOKUP_FH            72                                Read_attr        159 
OPEN_FH               7    $EXPREG           16        Write_attr        33 
READ                  1    $SETPRT            5                          
READBUFF              0                                Lookup           108 
READDIR_FH            2    $CLREF           169 
READLINK_FH           0    $SETEF           169        Extend             1 
REMDIR_FH             0                                                  
REMOVE_FH             0    $DCLAST          232        Delete             0 
RENAME_FH             0    $CLRAST            9        Enter              0 
SETATTR               8    $SETAST          360        Remove             0 
STATFS                1                                                  
SYMLINK_FH            0    $GETDVI            7        Read_V             9 
WRITE                41                                Write_V           57 
OTHER                 1    $CHKPRO           95                          
TOTAL               170                                                   
                                                                           

1. The summary of CFS services indicates the distribution of the CFS services. The OTHER category includes MAP, EXPORT, IMPORT, OPERATOR, STATUS, TRANSLATE, and UNMAP services.
2. The summary of OpenVMS system services idicates the consumption of various system services. Each service used by CFS is tallied with the addition of the subtotals for the $QIO system service. These totals are indicators of the XQP and disk performance.

The SHOW CFS/SUMMARY command provides a good indication of file system performance at the moment by providing the current and maximum values. See the DIGITAL TCP/IP Services for OpenVMS Management Command Reference manual for a description of the SHOW CFS/SUMMARY command.

Example 14-2 is an example of a SHOW CFS/SUMMARY display. The numbers in the example are keyed to the discussion that follows.

Example 14-2 SHOW CFS/SUMMARY Display

UCX> SHOW CFS /SUMMARY
 
 
                   CFS Service status and performance    21-MAR-1997 10:36:05.82 
(1)                                   (2)
Service State    Cur  Max    Total     Cacheop  Cur  Hit  I/O  Inc     Status 
---------------  ---  ---  ---------   ------- ---- ---- ---- ----  ------------ 
FP-Access          0    1        374   Read       0    0    0    0  Clusize   16 
FP-Attributes      0    1       2246   Read-A     0    0    0    0  Limit    256 
FP-Delete          0    0          0   Write      0    0    0    0  Inuse      0 
FP-Dir             0    1        989   Write-A    0    0    0    0  Busy       0 
FP-Rename          0    0          0   Write-D    0                 Hitrate    0 
  FP Sub_total     0    2       3609   (3)
Buffered           0    0          0   Nameop   Cur  Hit     Status 
Internal           0    1        127   ------  ---- ----  ------------- 
I/O                0    1         11   Add        0       Tabsize     0 
Lock               0    3         73   Delete     0       Inuse       0 
Logging            0    0          0   Lookup     0    0  Hitrate     0 
Resource           0    0          0   (4)
RMS                0    0          0   Fileop   Cur  Hit     Status 
Service            0    1          1   ------  ---- ----  ------------- 
Timer              0    1       1179   Find       0    0  Limit       0 
Other              0    0          0   Find-A          0  Inuse       0 
Synch              0    1        994   Find-C          0  Timeout     5 
                                                          Hitrate     0 
(5)                                                             
Services count     1    4       2863   ATCBs:4 TBABs:32 RDCBs:260 Pages:34(6)

1. The service state indicates the reason that a thread goes into a wait state. By determining where most of the waits occur, you can determine what in the system is slowing down the server.
2. The summary of data cache performance indicates how the file system cache is performing. This summary provides the current set of parameters:
   • Cluster size
   • Cache size limit (logical name UCX$CFS_CACHE_SIZE --- defined in the NFS server startup file SYS$STARTUP:UCX$NFS_SERVER_STARTUP.COM.)
   • How much of the cache is in use
   • How many I/O requests are outstanding
   • Overall hit rate of the cache
   
   All these values are related to cluster size (CLUSIZE) buffers. These buffers show the maximum number of blocks that can be read from or written to a disk.
   The read and write groups are synchronous, while Read-A and Write-A groups are asynchronous. The Write-D group is a deferred write operation, where the caller unmaps data without writing to disk. A UNIX-style file system frequently uses the Write-D group.
3. The summary of name cache performance provides the number of lookup operations saved by the name cache. The name cache converts a file-handle/name pair into another file handle which saves lookup operations because each entry found in the cache (a hit) saves a lookup operation.
4. The summary of file-attributes cache indicates how the attributes (file RDCB) cache is performing. The file-attributes cache values are described in Table 14-4.

   Table 14-4 File-Attributes Cache Values

   Value	Description
   Limit	Maximum number of resource descriptors and control blocks (RDCBs) that can be in cached status at any moment
   Inuse	Number of RDCBs in use
   Timeout	Number of seconds that any cached file's atributes are considered valid.
   Hit rate	Number of XQP QIOs (read attributes) that were saved because the valid RDCB was found (other overhead is also saved, for example, $ENQ/$DEQ time)

5. The summary of services and resources allocated provides the number of services and varying control blocks that are allocated. These services may not correspond one-for-one to NFS services because one service can call another to perform a special function. This is particularly true for container file systems, which make internal calls to certain operations in the OpenVMS space.
   The services and resources allocation values are described in Table 14-5.

   Table 14-5 Services and Resources Allocation Values

   Value	Description
   ATCBs	Asynchronous thread control blocks (one per thread)
   TBABs	Thread backout attachment blocks (one per active virtual lock)
   RDCBs	Resource description and control blocks (one per node, one per file system, one per file, one per cache buffer)
   Hit rate	Number of XQP QIOs (read attributes) that were saved because the valid RDCB was found (other overhead is also saved, for example, $ENQ/$DEQ time)

6. The pages from the virtual address space that are used dynamically when 512 bytes or less are needed for scratch space. A page also provides space for the record mapping table entries needed when accessing non-stream sequential files (record format conversion).

   14.13.3 Opening and Closing Files

   Because the NFS server does not maintain state about any of its clients, clients do not send explicit open and close file requests to the server. Instead, the server opens and closes the files for the clients. Any read or write request causes the server to open the file (if it does not already have the file open). The server caches the open files to create an internal state for each file within the NFS server environment.

   The server uses the following guidelines to close the files:

   • Closes the files that were not accessed during the specified time interval
   • Closes the oldest files when a user wants to access a new file and the maximum number of opened files for the NFS process or the maximum number of opened files specified in the OpenVMS account is reached.

   A short interval may cause the server to close files more often, thereby reducing performance. The default interval is 2 minutes. You can control the time interval by setting a new value for the UCX$NFS00000000_INACTIVITY logical name or with the /INACTIVITY_TIMER qualifier of the SET NFS SERVER command.

   14.13.4 Increasing the Number of Active Threads

   The NFS server is an asynchronous, multithreaded process, which means that multiple NFS requests can be processed concurrently. Each NFS request is referred to as a thread. With increased server activity, client users may experience timeout conditions. Assuming the server host has the available resources (CPU, memory, and disk speed), you can improve server response by increasing the number of active threads. You do this by changing the value for the UCX$NFS00000000_THREADS logical name. Use the SHOW NFS_SERVER command to display the maximum number of active threads.

   If you increase the number of active threads, you should also consider increasing the timeout period on UNIX clients. You do this with the timeo or /TIMEOUT option to the MOUNT command.

   If your clients still experience timeout conditions after increasing the number of active threads and the timout period on the client, you may need higher-performing hardware.

   14.13.5 Increasing the Size of the Host Table

   During NFS initialization, the server builds a host table from the proxy database file. If the number of client hosts listed in the proxy database exceeds the number specified with the UCX$NFS00000000_HOST logical name, the excess client host names will be ignored. This action has the effect of disabling access to the server for those client host names that cannot be loaded into the server's cache.

   Making the parameter value larger than needed causes NFS to allocate excess virtual memory within the server.

   14.13.6 Increasing the Size of the Transaction Cache

   Because NFS uses UDP as an underlying protocol, delivery between the client and the server is not guaranteed. Because delivery is not guaranteed, the client often reissues an NFS request if it does not receive a response from the server within a certain time period. This may cause CREATE, DELETE, LINK, RENAME, SYMLINK, and SETATTR operations to successfully complete the first time but fail the second time with a false error.

   Each server response to a client request is identified by the host name and a transaction identifier (XID). The server stores the responses it makes to any client requests for directory and file access. This way, whenever a client request is recognized as a duplicate, the server checks the response cache to see if a response has been sent. If it finds a matching response, the response is resent, otherwise, the duplicate request is ignored.

   If the the request is not a duplicate, the message is dispatched and processed.

   The size of the cache for these operations is limited by the value set with the UCX$NFS00000000_XID logical name. The default is 20, but you should increase this value if you notice any of the following situations on a client:

   • A file or link creation request returns "file exists," but the file did not exist when the file creation was requested and does exist after the file creation request.
   • A file/directory or link deletion request returns "no such file," but the file did exist, and does not exist after the deletion request.
   • A rename request returns "no such file," but the file did exist under its old name when the rename operation was requested and exists under its new name after the rename request.
   • A set attributes request returns "privilege violation," but the file can be written to by either the owner or group requester, and does exist after the request with the new attributes.
   • You increase the maximum number of threads.
   • You have not altered the client's timeo option to at least 20 (2.0 seconds).

   14.13.7 Improving Server Performance with XQP+

   The NFS server supports access to XQP+, the eXtended QIO processor file system enhancements introduced in OpenVMS Version 6.1. The XQP+ features are described in detail in the OpenVMS Version 6.1 New Features Manual.

   Performance improvements offered by XQP+ are especially beneficial for NFS servers that are handling a heavy load. By default, the XQP+ functionality is disabled; you must enable it by setting certain SYSGEN parameters.

   The file SYS$STARTUP:UCX$NFS_SERVER_STARTUP.COM describes how to enable OpenVMS and UCX-level usage of XQP+ features. The file also describes how to define logical names in SYS$STARTUP:UCX$SYSTARTUP.COM so that the site-specific choices are preserved across NFS and OpenVMS upgrades.

   The NFS server can take advantage of the following XQP+ features:

   • Improved file system concurrency.
     On a single system or in a cluster with all nodes running OpenVMS Version 6.1 or greater, you can enable XQP+ improved file system concurrency by setting the SYSGEN special parameter XQPCTL2 to 1 and then rebooting.
     As with all performance changes, make sure you understand the action of this configuration. For complete information about invoking the AUTOGEN command procedure to collect configuration information and rebooting your system, see the OpenVMS System Manager's Manual.
   • XQP+ threads, applicable for ODS--2 disks only
     To enable XQP+ threads:
     1. Set the SYSGEN parameter XQPCTLD1 to a number greater than 1. Because only executable images that specifically enable additional XQP+ threads use additional resources, it is usually safe to set the number to 8. The system manager should determine the specific value for each configuration, because XQPCTLD1 is a dynamic system parameter that takes effect immediately.
     2. Define the logical name UCX$CFS_ACP_ENABLE_THREADS as follows:

        $ DEFINE/SYSTEM/EXECUTIVE_MODE UCX$CFS_ACP_ENABLE_THREADS 1 
        

        
        The usual way to do this is to create, if necessary, the command procedure SYS$STARTUP:UCX$SYSTARTUP.COM, then edit the procedure appropriately.
     3. Shut down and restart the server for the change to take effect.
   • Performance enhancement through a change in the process of writing data to files.
     A write to a file on the OpenVMS operating system usually involves two operations: writing the actual data and updating the file header. When writes occur in rapid succession, it is possible to reduce the time taken to write the file by performing a series of data writes and then updating the file header once. The balancing risk is that information may be lost if the system crashes before the file header is updated.
     To cause the XQP to possibly defer file header writes, enter the following command:

     $ DEFINE/SYSTEM/EXEC UCX$CFS_ACP_ENABLE_DEFERRED_HEADER_WRITES 1 
      
     

     
     Be aware that this command allows the NFS call to return without waiting for certain file header operations to complete. This behavior is a technical violation of the NFS protocol, but it is common practice for some NFS vendors. If the system crashes before the file header completes, the data is written but may be inaccessible. Issue the following command from a suitably privileged account to return the file to a consistent state to determine whether the Analyze/Disk_Structure utility repairs errors that are detected in the file structure of a specified device:

     $ ANALYZE/DISK_STRUCTURE/REPAIR device
     

     
     This XQP+ feature offers a performance increase at the risk of data loss. DIGITAL strongly recommends against enabling this feature until you determine that the risk of data loss is acceptable. After enabling this feature, shut down and then restart the NFS server for the change to take effect.

The NFS server is started by the auxiliary server using the NFS server account UCX$NFS, which includes the NFS server process quotas and resource limits.

You can increase the NFS server account quotas and limits to improve the performance of the NFS server. Use the OpenVMS Authorize utility to change the quotas and limits for the UCX$NFS account.

14.13.9 Increasing UAF File Limits

A file limit (FILLM) quota is associated with each OpenVMS user account. The FILLM quota specifies the maximum number of files that can be accessed simultaneously. If a file is accessed to process a read or write request, the file access cannot exceed the FILLM quota specified in the OpenVMS user's authorization information. To make this file limit transparent to the client, NFS closes the least-recently-accessed file and accesses the new file. When this happens, the error log file contains an "exceeded quota" message.

Because the open files quota information is loaded into the NFS server upon startup, changes to a user's authorization information do not take effect until you restart the NFS server.

An FILLM quota is also associated with the NFS server account. If the FILLM quota is set too low, it degrades the server's performance. Set this quota so it is large enough to accommodate the total of all the individual NFS users' quotas.

Under normal situations, the NFS request is successfully completed after you reset the quota limitation. The inactivity timer interval can reduce the required open files quota by closing old files automatically before the contention.