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diff --git a/docs/docbook/projdoc/locking.xml b/docs/docbook/projdoc/locking.xml deleted file mode 100644 index 8bdb06ca8f..0000000000 --- a/docs/docbook/projdoc/locking.xml +++ /dev/null @@ -1,1061 +0,0 @@ -<chapter id="locking"> -<chapterinfo> - &author.jeremy; - &author.jelmer; - &author.jht; - &author.eroseme; -</chapterinfo> -<title>File and Record Locking</title> - -<para> -One area that causes trouble for many network administrators is locking. -The extent of the problem is readily evident from searches over the Internet. -</para> - -<sect1> -<title>Features and Benefits</title> - -<para> -Samba provides all the same locking semantics that MS Windows clients expect -and that MS Windows NT4/200x servers also provide. -</para> - -<para> -The term <emphasis>locking</emphasis> has exceptionally broad meaning and covers -a range of functions that are all categorized under this one term. -</para> - -<para> -Opportunistic locking is a desirable feature when it can enhance the -perceived performance of applications on a networked client. However, the -opportunistic locking protocol is not robust and, therefore, can -encounter problems when invoked beyond a simplistic configuration or -on extended slow or faulty networks. In these cases, operating -system management of opportunistic locking and/or recovering from -repetitive errors can offset the perceived performance advantage that -it is intended to provide. -</para> - -<para> -The MS Windows network administrator needs to be aware that file and record -locking semantics (behavior) can be controlled either in Samba or by way of registry -settings on the MS Windows client. -</para> - -<note> -<para> -Sometimes it is necessary to disable locking control settings on both the Samba -server as well as on each MS Windows client! -</para> -</note> - -</sect1> - -<sect1> -<title>Discussion</title> - -<para> -There are two types of locking that need to be performed by an SMB server. -The first is <emphasis>record locking</emphasis> that allows a client to lock -a range of bytes in a open file. The second is the <emphasis>deny modes</emphasis> -that are specified when a file is open. -</para> - -<para> -Record locking semantics under UNIX are very different from record locking under -Windows. Versions of Samba before 2.2 have tried to use the native fcntl() UNIX -system call to implement proper record locking between different Samba clients. -This cannot be fully correct for several reasons. The simplest is the fact -that a Windows client is allowed to lock a byte range up to 2^32 or 2^64, -depending on the client OS. The UNIX locking only supports byte ranges up to 2^31. -So it is not possible to correctly satisfy a lock request above 2^31. There are -many more differences, too many to be listed here. -</para> - -<para> -Samba 2.2 and above implements record locking completely independent of the -underlying UNIX system. If a byte range lock that the client requests happens -to fall into the range of 0-2^31, Samba hands this request down to the UNIX system. -All other locks cannot be seen by UNIX, anyway. -</para> - -<para> -Strictly speaking, an SMB server should check for locks before every read and write call on -a file. Unfortunately with the way fcntl() works, this can be slow and may overstress -the <command>rpc.lockd</command>. This is almost always unnecessary as clients are supposed to -independently make locking calls before reads and writes if locking is -important to them. By default, Samba only makes locking calls when explicitly asked -to by a client, but if you set <smbconfoption><name>strict locking</name><value>yes</value></smbconfoption>, it -will make lock checking calls on <emphasis>every</emphasis> read and write call. -</para> - -<para> -You can also disable byte range locking completely by using -<smbconfoption><name>locking</name><value>no</value></smbconfoption>. -This is useful for those shares that do not support locking or do not need it -(such as CDROMs). In this case, Samba fakes the return codes of locking calls to -tell clients that everything is okay. -</para> - -<para> -The second class of locking is the <emphasis>deny modes</emphasis>. These -are set by an application when it opens a file to determine what types of -access should be allowed simultaneously with its open. A client may ask for -<constant>DENY_NONE</constant>, <constant>DENY_READ</constant>, -<constant>DENY_WRITE</constant>, or <constant>DENY_ALL</constant>. There are also special compatibility -modes called <constant>DENY_FCB</constant> and <constant>DENY_DOS</constant>. -</para> - -<sect2> -<title>Opportunistic Locking Overview</title> - -<para> -Opportunistic locking (Oplocks) is invoked by the Windows file system -(as opposed to an API) via registry entries (on the server and the client) -for the purpose of enhancing network performance when accessing a file -residing on a server. Performance is enhanced by caching the file -locally on the client that allows: -</para> - -<variablelist> - <varlistentry><term>Read-ahead:</term> - <listitem><para> - The client reads the local copy of the file, eliminating network latency. - </para></listitem> - </varlistentry> - - <varlistentry><term>Write caching:</term> - <listitem><para> - The client writes to the local copy of the file, eliminating network latency. - </para></listitem> - </varlistentry> - - <varlistentry><term>Lock caching:</term> - <listitem><para> - The client caches application locks locally, eliminating network latency. - </para></listitem> - </varlistentry> -</variablelist> - -<para> -The performance enhancement of oplocks is due to the opportunity of -exclusive access to the file &smbmdash; even if it is opened with deny-none &smbmdash; -because Windows monitors the file's status for concurrent access from -other processes. -</para> - -<variablelist> -<title>Windows defines 4 kinds of Oplocks:</title> - - <varlistentry><term>Level1 Oplock</term> - <listitem><para> - The redirector sees that the file was opened with deny - none (allowing concurrent access), verifies that no - other process is accessing the file, checks that - oplocks are enabled, then grants deny-all/read-write/exclusive - access to the file. The client now performs - operations on the cached local file. - </para> - - <para> - If a second process attempts to open the file, the open - is deferred while the redirector <quote>breaks</quote> the original - oplock. The oplock break signals the caching client to - write the local file back to the server, flush the - local locks and discard read-ahead data. The break is - then complete, the deferred open is granted, and the - multiple processes can enjoy concurrent file access as - dictated by mandatory or byte-range locking options. - However, if the original opening process opened the - file with a share mode other than deny-none, then the - second process is granted limited or no access, despite - the oplock break. - </para></listitem> - </varlistentry> - - <varlistentry><term>Level2 Oplock</term> - <listitem><para> - Performs like a Level1 oplock, except caching is only - operative for reads. All other operations are performed - on the server disk copy of the file. - </para></listitem> - </varlistentry> - - <varlistentry><term>Filter Oplock</term> - <listitem><para> - Does not allow write or delete file access. - </para></listitem> - </varlistentry> - - <varlistentry><term>Batch Oplock</term> - <listitem><para> - Manipulates file openings and closings and allows caching - of file attributes. - </para></listitem> - </varlistentry> -</variablelist> - -<para> -An important detail is that oplocks are invoked by the file system, not -an application API. Therefore, an application can close an oplocked -file, but the file system does not relinquish the oplock. When the -oplock break is issued, the file system then simply closes the file in -preparation for the subsequent open by the second process. -</para> - -<para> -<emphasis>Opportunistic locking</emphasis> is actually an improper name for this feature. -The true benefit of this feature is client-side data caching, and -oplocks is merely a notification mechanism for writing data back to the -networked storage disk. The limitation of opportunistic locking is the -reliability of the mechanism to process an oplock break (notification) -between the server and the caching client. If this exchange is faulty -(usually due to timing out for any number of reasons), then the -client-side caching benefit is negated. -</para> - -<para> -The actual decision that a user or administrator should consider is -whether it is sensible to share among multiple users data that will -be cached locally on a client. In many cases the answer is no. -Deciding when to cache or not cache data is the real question, and thus -<quote>opportunistic locking</quote> should be treated as a toggle for client-side -caching. Turn it <quote>on</quote> when client-side caching is desirable and -reliable. Turn it <quote>off</quote> when client-side caching is redundant, -unreliable or counter-productive. -</para> - -<para> -Opportunistic locking is by default set to <quote>on</quote> by Samba on all -configured shares, so careful attention should be given to each case to -determine if the potential benefit is worth the potential for delays. -The following recommendations will help to characterize the environment -where opportunistic locking may be effectively configured. -</para> - -<para> -Windows opportunistic locking is a lightweight performance-enhancing -feature. It is not a robust and reliable protocol. Every -implementation of opportunistic locking should be evaluated as a -tradeoff between perceived performance and reliability. Reliability -decreases as each successive rule above is not enforced. Consider a -share with oplocks enabled, over a wide area network, to a client on a -South Pacific atoll, on a high-availability server, serving a -mission-critical multi-user corporate database during a tropical -storm. This configuration will likely encounter problems with oplocks. -</para> - -<para> -Oplocks can be beneficial to perceived client performance when treated -as a configuration toggle for client-side data caching. If the data -caching is likely to be interrupted, then oplock usage should be -reviewed. Samba enables opportunistic locking by default on all -shares. Careful attention should be given to the client usage of -shared data on the server, the server network reliability and the -opportunistic locking configuration of each share. -In mission critical high availability environments, data integrity is -often a priority. Complex and expensive configurations are implemented -to ensure that if a client loses connectivity with a file server, a -failover replacement will be available immediately to provide -continuous data availability. -</para> - -<para> -Windows client failover behavior is more at risk of application -interruption than other platforms because it is dependent upon an -established TCP transport connection. If the connection is interrupted -&smbmdash; as in a file server failover &smbmdash; a new session must be established. -It is rare for Windows client applications to be coded to recover -correctly from a transport connection loss, therefore, most applications -will experience some sort of interruption &smbmdash; at worst, abort and -require restarting. -</para> - -<para> -If a client session has been caching writes and reads locally due to -opportunistic locking, it is likely that the data will be lost when the -application restarts or recovers from the TCP interrupt. When the TCP -connection drops, the client state is lost. When the file server -recovers, an oplock break is not sent to the client. In this case, the -work from the prior session is lost. Observing this scenario with -oplocks disabled and with the client writing data to the file server -real-time, the failover will provide the data on disk as it -existed at the time of the disconnect. -</para> - -<para> -In mission-critical high-availability environments, careful attention -should be given to opportunistic locking. Ideally, comprehensive -testing should be done with all affected applications with oplocks -enabled and disabled. -</para> - -<sect3> -<title>Exclusively Accessed Shares</title> - -<para> -Opportunistic locking is most effective when it is confined to shares -that are exclusively accessed by a single user, or by only one user at -a time. Because the true value of opportunistic locking is the local -client caching of data, any operation that interrupts the caching -mechanism will cause a delay. -</para> - -<para> -Home directories are the most obvious examples of where the performance -benefit of opportunistic locking can be safely realized. -</para> - -</sect3> - -<sect3> -<title>Multiple-Accessed Shares or Files</title> - -<para> -As each additional user accesses a file in a share with opportunistic -locking enabled, the potential for delays and resulting perceived poor -performance increases. When multiple users are accessing a file on a -share that has oplocks enabled, the management impact of sending and -receiving oplock breaks and the resulting latency while other clients -wait for the caching client to flush data offset the performance gains -of the caching user. -</para> - -<para> -As each additional client attempts to access a file with oplocks set, -the potential performance improvement is negated and eventually results -in a performance bottleneck. -</para> - -</sect3> - -<sect3> -<title>UNIX or NFS Client-Accessed Files</title> - -<para> -Local UNIX and NFS clients access files without a mandatory -file-locking mechanism. Thus, these client platforms are incapable of -initiating an oplock break request from the server to a Windows client -that has a file cached. Local UNIX or NFS file access can therefore -write to a file that has been cached by a Windows client, which -exposes the file to likely data corruption. -</para> - -<para> -If files are shared between Windows clients, and either local UNIX -or NFS users, turn opportunistic locking off. -</para> - -</sect3> - -<sect3> -<title>Slow and/or Unreliable Networks</title> - -<para> -The biggest potential performance improvement for opportunistic locking -occurs when the client-side caching of reads and writes delivers the -most differential over sending those reads and writes over the wire. -This is most likely to occur when the network is extremely slow, -congested, or distributed (as in a WAN). However, network latency also -has a high impact on the reliability of the oplock break -mechanism, and thus increases the likelihood of encountering oplock -problems that more than offset the potential perceived performance -gain. Of course, if an oplock break never has to be sent, then this is -the most advantageous scenario to utilize opportunistic locking. -</para> - -<para> -If the network is slow, unreliable, or a WAN, then do not configure -opportunistic locking if there is any chance of multiple users -regularly opening the same file. -</para> - -</sect3> - -<sect3> -<title>Multi-User Databases</title> - -<para> -Multi-user databases clearly pose a risk due to their very nature &smbmdash; -they are typically heavily accessed by numerous users at random -intervals. Placing a multi-user database on a share with opportunistic -locking enabled will likely result in a locking management bottleneck -on the Samba server. Whether the database application is developed -in-house or a commercially available product, ensure that the share -has opportunistic locking disabled. -</para> - -</sect3> - -<sect3> -<title>PDM Data Shares</title> - -<para> -Process Data Management (PDM) applications such as IMAN, Enovia and -Clearcase are increasing in usage with Windows client platforms, and -therefore SMB datastores. PDM applications manage multi-user -environments for critical data security and access. The typical PDM -environment is usually associated with sophisticated client design -applications that will load data locally as demanded. In addition, the -PDM application will usually monitor the data-state of each client. -In this case, client-side data caching is best left to the local -application and PDM server to negotiate and maintain. It is -appropriate to eliminate the client OS from any caching tasks, and the -server from any oplock management, by disabling opportunistic locking on -the share. -</para> - -</sect3> - -<sect3> -<title>Beware of Force User</title> - -<para> -Samba includes an &smb.conf; parameter called <smbconfoption><name>force user</name></smbconfoption> that changes -the user accessing a share from the incoming user to whatever user is -defined by the smb.conf variable. If opportunistic locking is enabled -on a share, the change in user access causes an oplock break to be sent -to the client, even if the user has not explicitly loaded a file. In -cases where the network is slow or unreliable, an oplock break can -become lost without the user even accessing a file. This can cause -apparent performance degradation as the client continually reconnects -to overcome the lost oplock break. -</para> - -<para> -Avoid the combination of the following: -</para> - -<itemizedlist> - <listitem><para> - <smbconfoption><name>force user</name></smbconfoption> in the &smb.conf; share configuration. - </para></listitem> - - <listitem><para> - Slow or unreliable networks - </para></listitem> - - <listitem><para> - Opportunistic locking enabled - </para></listitem> -</itemizedlist> - -</sect3> - -<sect3> -<title>Advanced Samba Opportunistic Locking Parameters</title> - -<para> -Samba provides opportunistic locking parameters that allow the -administrator to adjust various properties of the oplock mechanism to -account for timing and usage levels. These parameters provide good -versatility for implementing oplocks in environments where they would -likely cause problems. The parameters are: -<smbconfoption><name>oplock break wait time</name></smbconfoption>, -<smbconfoption><name>oplock contention limit</name></smbconfoption>. -</para> - -<para> -For most users, administrators and environments, if these parameters -are required, then the better option is to simply turn oplocks off. -The Samba SWAT help text for both parameters reads: <quote>Do not change -this parameter unless you have read and understood the Samba oplock code.</quote> -This is good advice. -</para> - -</sect3> - -<sect3> -<title>Mission-Critical High-Availability</title> - -<para> -In mission-critical high-availability environments, data integrity is -often a priority. Complex and expensive configurations are implemented -to ensure that if a client loses connectivity with a file server, a -failover replacement will be available immediately to provide -continuous data availability. -</para> - -<para> -Windows client failover behavior is more at risk of application -interruption than other platforms because it is dependant upon an -established TCP transport connection. If the connection is interrupted -&smbmdash; as in a file server failover &smbmdash; a new session must be established. -It is rare for Windows client applications to be coded to recover -correctly from a transport connection loss, therefore, most applications -will experience some sort of interruption &smbmdash; at worst, abort and -require restarting. -</para> - -<para> -If a client session has been caching writes and reads locally due to -opportunistic locking, it is likely that the data will be lost when the -application restarts, or recovers from the TCP interrupt. When the TCP -connection drops, the client state is lost. When the file server -recovers, an oplock break is not sent to the client. In this case, the -work from the prior session is lost. Observing this scenario with -oplocks disabled, and the client was writing data to the file server -real-time, then the failover will provide the data on disk as it -existed at the time of the disconnect. -</para> - -<para> -In mission-critical high-availability environments, careful attention -should be given to opportunistic locking. Ideally, comprehensive -testing should be done with all effected applications with oplocks -enabled and disabled. -</para> - -</sect3> -</sect2> -</sect1> - -<sect1> -<title>Samba Opportunistic Locking Control</title> - -<para> -Opportunistic locking is a unique Windows file locking feature. It is -not really file locking, but is included in most discussions of Windows -file locking, so is considered a de facto locking feature. -Opportunistic locking is actually part of the Windows client file -caching mechanism. It is not a particularly robust or reliable feature -when implemented on the variety of customized networks that exist in -enterprise computing. -</para> - -<para> -Like Windows, Samba implements opportunistic locking as a server-side -component of the client caching mechanism. Because of the lightweight -nature of the Windows feature design, effective configuration of -opportunistic locking requires a good understanding of its limitations, -and then applying that understanding when configuring data access for -each particular customized network and client usage state. -</para> - -<para> -Opportunistic locking essentially means that the client is allowed to download and cache -a file on their hard drive while making changes; if a second client wants to access the -file, the first client receives a break and must synchronize the file back to the server. -This can give significant performance gains in some cases; some programs insist on -synchronizing the contents of the entire file back to the server for a single change. -</para> - -<para> -Level1 Oplocks (also known as just plain <quote>oplocks</quote>) is another term for opportunistic locking. -</para> - -<para> -Level2 Oplocks provides opportunistic locking for a file that will be treated as -<emphasis>read only</emphasis>. Typically this is used on files that are read-only or -on files that the client has no initial intention to write to at time of opening the file. -</para> - -<para> -Kernel Oplocks are essentially a method that allows the Linux kernel to co-exist with -Samba's oplocked files, although this has provided better integration of MS Windows network -file locking with the underlying OS, SGI IRIX and Linux are the only two OSs that are -oplock-aware at this time. -</para> - -<para> -Unless your system supports kernel oplocks, you should disable oplocks if you are -accessing the same files from both UNIX/Linux and SMB clients. Regardless, oplocks should -always be disabled if you are sharing a database file (e.g., Microsoft Access) between -multiple clients, as any break the first client receives will affect synchronization of -the entire file (not just the single record), which will result in a noticeable performance -impairment and, more likely, problems accessing the database in the first place. Notably, -Microsoft Outlook's personal folders (*.pst) react quite badly to oplocks. If in doubt, -disable oplocks and tune your system from that point. -</para> - -<para> -If client-side caching is desirable and reliable on your network, you will benefit from -turning on oplocks. If your network is slow and/or unreliable, or you are sharing your -files among other file sharing mechanisms (e.g., NFS) or across a WAN, or multiple people -will be accessing the same files frequently, you probably will not benefit from the overhead -of your client sending oplock breaks and will instead want to disable oplocks for the share. -</para> - -<para> -Another factor to consider is the perceived performance of file access. If oplocks provide no -measurable speed benefit on your network, it might not be worth the hassle of dealing with them. -</para> - -<sect2> -<title>Example Configuration</title> - -<para> -In the following section we examine two distinct aspects of Samba locking controls. -</para> - -<sect3> -<title>Disabling Oplocks</title> - -<para> -You can disable oplocks on a per-share basis with the following: -</para> - -<para> -<smbconfblock> -<smbconfsection>[acctdata]</smbconfsection> -<smbconfoption><name>oplocks</name><value>False</value></smbconfoption> -<smbconfoption><name>level2 oplocks</name><value>False</value></smbconfoption> -</smbconfblock> -</para> - -<para> -The default oplock type is Level1. Level2 oplocks are enabled on a per-share basis -in the &smb.conf; file. -</para> - -<para> -Alternately, you could disable oplocks on a per-file basis within the share: -</para> - -<para> - <smbconfblock> -<smbconfoption><name>veto oplock files</name><value>/*.mdb/*.MDB/*.dbf/*.DBF/</value></smbconfoption> -</smbconfblock> -</para> - -<para> -If you are experiencing problems with oplocks as apparent from Samba's log entries, -you may want to play it safe and disable oplocks and Level2 oplocks. -</para> - -</sect3> - -<sect3> -<title>Disabling Kernel Oplocks</title> - -<para> -Kernel oplocks is an &smb.conf; parameter that notifies Samba (if -the UNIX kernel has the capability to send a Windows client an oplock -break) when a UNIX process is attempting to open the file that is -cached. This parameter addresses sharing files between UNIX and -Windows with oplocks enabled on the Samba server: the UNIX process -can open the file that is Oplocked (cached) by the Windows client and -the smbd process will not send an oplock break, which exposes the file -to the risk of data corruption. If the UNIX kernel has the ability to -send an oplock break, then the kernel oplocks parameter enables Samba -to send the oplock break. Kernel oplocks are enabled on a per-server -basis in the &smb.conf; file. -</para> - -<para> -<smbconfblock> -<smbconfoption><name>kernel oplocks</name><value>yes</value></smbconfoption> -</smbconfblock> -The default is no. -</para> - -<para> -Veto opLocks is an &smb.conf; parameter that identifies specific files for -which oplocks are disabled. When a Windows client opens a file that -has been configured for veto oplocks, the client will not be granted -the oplock, and all operations will be executed on the original file on -disk instead of a client-cached file copy. By explicitly identifying -files that are shared with UNIX processes and disabling oplocks for -those files, the server-wide Oplock configuration can be enabled to -allow Windows clients to utilize the performance benefit of file -caching without the risk of data corruption. Veto Oplocks can be -enabled on a per-share basis, or globally for the entire server, in the -&smb.conf; file as shown in <link linkend="far1"/>. -</para> - -<para> -<smbconfexample id="far1"> -<title>Share with some files oplocked</title> -<smbconfsection>[global]</smbconfsection> -<smbconfoption><name>veto oplock files</name><value>/filename.htm/*.txt/</value></smbconfoption> - -<smbconfsection>[share_name]</smbconfsection> -<smbconfoption><name>veto oplock files</name><value>/*.exe/filename.ext/</value></smbconfoption> -</smbconfexample> -</para> - -<para> -<smbconfoption><name>oplock break wait time</name></smbconfoption> is an &smb.conf; parameter -that adjusts the time interval for Samba to reply to an oplock break request. Samba recommends: -<quote>Do not change this parameter unless you have read and understood the Samba oplock code.</quote> -Oplock break Wait Time can only be configured globally in the &smb.conf; file as shown below. -</para> - -<para> - <smbconfblock> -<smbconfoption><name>oplock break wait time</name><value> 0 (default)</value></smbconfoption> -</smbconfblock> -</para> - -<para> -<emphasis>Oplock break contention limit</emphasis> is an &smb.conf; parameter that limits the -response of the Samba server to grant an oplock if the configured -number of contending clients reaches the limit specified by the parameter. Samba recommends -<quote>Do not change this parameter unless you have read and understood the Samba oplock code.</quote> -Oplock break Contention Limit can be enable on a per-share basis, or globally for -the entire server, in the &smb.conf; file as shown in <link linkend="far3"/>. -</para> - -<para> -<smbconfexample id="far3"> - <title>Configuration with oplock break contention limit</title> -<smbconfsection>[global]</smbconfsection> -<smbconfoption><name>oplock break contention limit</name><value> 2 (default)</value></smbconfoption> - -<smbconfsection>[share_name]</smbconfsection> -<smbconfoption><name>oplock break contention limit</name><value> 2 (default)</value></smbconfoption> -</smbconfexample> -</para> - -</sect3> -</sect2> - -</sect1> - -<sect1> -<title>MS Windows Opportunistic Locking and Caching Controls</title> - -<para> -There is a known issue when running applications (like Norton Anti-Virus) on a Windows 2000/ XP -workstation computer that can affect any application attempting to access shared database files -across a network. This is a result of a default setting configured in the Windows 2000/XP -operating system known as <emphasis>opportunistic locking</emphasis>. When a workstation -attempts to access shared data files located on another Windows 2000/XP computer, -the Windows 2000/XP operating system will attempt to increase performance by locking the -files and caching information locally. When this occurs, the application is unable to -properly function, which results in an <quote>Access Denied</quote> - error message being displayed during network operations. -</para> - -<para> -All Windows operating systems in the NT family that act as database servers for data files -(meaning that data files are stored there and accessed by other Windows PCs) may need to -have opportunistic locking disabled in order to minimize the risk of data file corruption. -This includes Windows 9x/Me, Windows NT, Windows 200x, and Windows XP. -</para> - -<para> -If you are using a Windows NT family workstation in place of a server, you must also -disable opportunistic locking (oplocks) on that workstation. For example, if you use a -PC with the Windows NT Workstation operating system instead of Windows NT Server, and you -have data files located on it that are accessed from other Windows PCs, you may need to -disable oplocks on that system. -</para> - -<para> -The major difference is the location in the Windows registry where the values for disabling -oplocks are entered. Instead of the LanManServer location, the LanManWorkstation location -may be used. -</para> - -<para> -You can verify (change or add, if necessary) this registry value using the Windows -Registry Editor. When you change this registry value, you will have to reboot the PC -to ensure that the new setting goes into effect. -</para> - -<para> -The location of the client registry entry for opportunistic locking has changed in -Windows 2000 from the earlier location in Microsoft Windows NT. -</para> - -<note><para> -Windows 2000 will still respect the EnableOplocks registry value used to disable oplocks -in earlier versions of Windows. -</para></note> - -<para> -You can also deny the granting of opportunistic locks by changing the following registry entries: -</para> - -<para> -<programlisting> - HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\MRXSmb\Parameters\ - - OplocksDisabled REG_DWORD 0 or 1 - Default: 0 (not disabled) -</programlisting> -</para> - -<note><para> -The OplocksDisabled registry value configures Windows clients to either request or not -request opportunistic locks on a remote file. To disable oplocks, the value of - OplocksDisabled must be set to 1. -</para></note> - -<para> -<programlisting> - HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\LanmanServer\Parameters - - EnableOplocks REG_DWORD 0 or 1 - Default: 1 (Enabled by Default) - - EnableOpLockForceClose REG_DWORD 0 or 1 - Default: 0 (Disabled by Default) -</programlisting> -</para> - -<note><para> -The EnableOplocks value configures Windows-based servers (including Workstations sharing -files) to allow or deny opportunistic locks on local files. -</para></note> - -<para> -To force closure of open oplocks on close or program exit, EnableOpLockForceClose must be set to 1. -</para> - -<para> -An illustration of how Level2 oplocks work: -</para> - -<itemizedlist> - <listitem><para> - Station 1 opens the file requesting oplock. - </para></listitem> - <listitem><para> - Since no other station has the file open, the server grants station 1 exclusive oplock. - </para></listitem> - <listitem><para> - Station 2 opens the file requesting oplock. - </para></listitem> - <listitem><para> - Since station 1 has not yet written to the file, the server asks station 1 to break - to Level2 oplock. - </para></listitem> - <listitem><para> - Station 1 complies by flushing locally buffered lock information to the server. - </para></listitem> - <listitem><para> - Station 1 informs the server that it has Broken to Level2 Oplock (alternately, - station 1 could have closed the file). - </para></listitem> - <listitem><para> - The server responds to station 2's open request, granting it Level2 oplock. - Other stations can likewise open the file and obtain Level2 oplock. - </para></listitem> - <listitem><para> - Station 2 (or any station that has the file open) sends a write request SMB. - The server returns the write response. - </para></listitem> - <listitem><para> - The server asks all stations that have the file open to break to none, meaning no - station holds any oplock on the file. Because the workstations can have no cached - writes or locks at this point, they need not respond to the break-to-none advisory; - all they need do is invalidate locally cashed read-ahead data. - </para></listitem> -</itemizedlist> - -<sect2> -<title>Workstation Service Entries</title> - -<para><programlisting> - \HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\LanmanWorkstation\Parameters - - UseOpportunisticLocking REG_DWORD 0 or 1 - Default: 1 (true) -</programlisting></para> - -<para> -This indicates whether the redirector should use opportunistic-locking (oplock) performance -enhancement. This parameter should be disabled only to isolate problems. -</para> - -</sect2> -<sect2> -<title>Server Service Entries</title> - -<para><programlisting> - \HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\LanmanServer\Parameters - - EnableOplocks REG_DWORD 0 or 1 - Default: 1 (true) -</programlisting></para> - -<para> -This specifies whether the server allows clients to use oplocks on files. Oplocks are a -significant performance enhancement, but have the potential to cause lost cached -data on some networks, particularly wide area networks. -</para> - -<para><programlisting> - MinLinkThroughput REG_DWORD 0 to infinite bytes per second - Default: 0 -</programlisting></para> - -<para> -This specifies the minimum link throughput allowed by the server before it disables -raw and opportunistic locks for this connection. -</para> - -<para><programlisting> - MaxLinkDelay REG_DWORD 0 to 100,000 seconds - Default: 60 -</programlisting></para> - -<para> -This specifies the maximum time allowed for a link delay. If delays exceed this number, -the server disables raw I/O and opportunistic locking for this connection. -</para> - -<para><programlisting> - OplockBreakWait REG_DWORD 10 to 180 seconds - Default: 35 -</programlisting></para> - -<para> -This 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. -</para> - -</sect2> -</sect1> - -<sect1> -<title>Persistent Data Corruption</title> - -<para> -If you have applied all of the settings discussed in this chapter but data corruption problems -and other symptoms persist, here are some additional things to check out. -</para> - -<para> -We have credible reports from developers that faulty network hardware, such as a single -faulty network card, can cause symptoms similar to read caching and data corruption. -If you see persistent data corruption even after repeated reindexing, you may have to -rebuild the data files in question. This involves creating a new data file with the -same definition as the file to be rebuilt and transferring the data from the old file -to the new one. There are several known methods for doing this that can be found in -our Knowledge Base. -</para> - -</sect1> - -<sect1> -<title>Common Errors</title> - -<para> -In some sites, locking problems surface as soon as a server is installed; in other sites -locking problems may not surface for a long time. Almost without exception, when a locking -problem does surface it will cause embarrassment and potential data corruption. -</para> - -<para> -Over the past few years there have been a number of complaints on the Samba mailing lists -that have claimed that Samba caused data corruption. Three causes have been identified -so far: -</para> - -<itemizedlist> - <listitem><para> - Incorrect configuration of opportunistic locking (incompatible with the application - being used. This is a common problem even where MS Windows NT4 or MS Windows - 200x-based servers were in use. It is imperative that the software application vendors' - instructions for configuration of file locking should be followed. If in doubt, - disable oplocks on both the server and the client. Disabling of all forms of file - caching on the MS Windows client may be necessary also. - </para></listitem> - - <listitem><para> - Defective network cards, cables, or HUBs/Switched. This is generally a more - prevalent factor with low cost networking hardware, although occasionally there - have also been problems with incompatibilities in more up-market hardware. - </para></listitem> - - <listitem><para> - There have been some random reports of Samba log files being written over data - files. This has been reported by very few sites (about five in the past three years) - and all attempts to reproduce the problem have failed. The Samba Team has been - unable to catch this happening and thus has not been able to isolate any particular - cause. Considering the millions of systems that use Samba, for the sites that have - been affected by this as well as for the Samba Team this is a frustrating and - a vexing challenge. If you see this type of thing happening, please create a bug - report on Samba <ulink url="https://bugzilla.samba.org">Bugzilla</ulink> without delay. - Make sure that you give as much information as you possibly can help isolate the - cause and to allow replication of the problem (an essential step in problem isolation and correction). - </para></listitem> -</itemizedlist> - - <sect2> - <title>locking.tdb Error Messages</title> - - <para> - <quote> - We are seeing lots of errors in the Samba logs, like: -<programlisting> -tdb(/usr/local/samba_2.2.7/var/locks/locking.tdb): rec_read bad magic - 0x4d6f4b61 at offset=36116 -</programlisting> - - What do these mean? - </quote> - </para> - - <para> - This error indicated a corrupted tdb. Stop all instances of smbd, delete locking.tdb, and restart smbd. - </para> - - </sect2> - - <sect2> - <title>Problems Saving Files in MS Office on Windows XP</title> - - <para>This is a bug in Windows XP. More information can be - found in <ulink url="http://support.microsoft.com/?id=812937">Microsoft Knowledge Base article 812937.</ulink></para> - - </sect2> - - <sect2> - - <title>Long Delays Deleting Files Over Network with XP SP1</title> - - <para><quote>It sometimes takes approximately 35 seconds to delete files over the network after XP SP1 has been applied.</quote></para> - - <para>This is a bug in Windows XP. More information can be found in <ulink url="http://support.microsoft.com/?id=811492"> - Microsoft Knowledge Base article 811492.</ulink></para> - </sect2> - -</sect1> - -<sect1> -<title>Additional Reading</title> - -<para> -You may want to check for an updated version of this white paper on our Web site from -time to time. Many of our white papers are updated as information changes. For those papers, -the last edited date is always at the top of the paper. -</para> - -<para> -Section of the Microsoft MSDN Library on opportunistic locking: -</para> - -<para> -Opportunistic Locks, Microsoft Developer Network (MSDN), Windows Development > -Windows Base Services > Files and I/O > SDK Documentation > File Storage > File Systems -> About File Systems > Opportunistic Locks, Microsoft Corporation. -<ulink noescape="1" url="http://msdn.microsoft.com/library/en-us/fileio/storage_5yk3.asp">http://msdn.microsoft.com/library/en-us/fileio/storage_5yk3.asp</ulink> -</para> - -<para> - Microsoft Knowledge Base Article Q224992 <?latex \linebreak ?><quote>Maintaining Transactional Integrity -with OPLOCKS</quote>, -Microsoft Corporation, April 1999, <ulink noescape="1" url="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q224992">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q224992</ulink>. -</para> - -<para> -Microsoft Knowledge Base Article Q296264 <quote>Configuring Opportunistic Locking in Windows 2000</quote>, -Microsoft Corporation, April 2001, <ulink noescape="1" url="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q296264">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q296264</ulink>. -</para> - -<para> -Microsoft Knowledge Base Article Q129202 <quote>PC Ext: Explanation of Opportunistic Locking on Windows NT</quote>, -Microsoft Corporation, April 1995, <ulink noescape="1" url="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q129202">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q129202</ulink>. -</para> - -</sect1> -</chapter> |