diff options
Diffstat (limited to 'docs/howto/locking.xml')
| -rw-r--r-- | docs/howto/locking.xml | 1063 |
1 files changed, 1063 insertions, 0 deletions
diff --git a/docs/howto/locking.xml b/docs/howto/locking.xml new file mode 100644 index 0000000000..636b0dfd68 --- /dev/null +++ b/docs/howto/locking.xml @@ -0,0 +1,1063 @@ +<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 +fail-over replacement will be available immediately to provide +continuous data availability. +</para> + +<para> +Windows client fail-over 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 fail-over &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 fail-over 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 data-stores. 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 +fail-over replacement will be available immediately to provide +continuous data availability. +</para> + +<para> +Windows client fail-over 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 fail-over &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 fail-over 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. +<footnote><para>Microsoft has documented this in Knowledge Base article 300216.</para></footnote> +</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 re-indexing, 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> |