diff options
| author | Jelmer Vernooij <jelmer@samba.org> | 2003-08-13 06:07:10 +0000 |
|---|---|---|
| committer | Jelmer Vernooij <jelmer@samba.org> | 2003-08-13 06:07:10 +0000 |
| commit | f62eaeb1a5add34ee7353d0d95db3c84a5c71c22 (patch) | |
| tree | 10cf7e89e5a1ec800b7f30f731cbd4f4ebf5f13d /docs/htmldocs/locking.html | |
| parent | 879573e127150d258bc7ad9526f273c9c846da99 (diff) | |
| download | samba-f62eaeb1a5add34ee7353d0d95db3c84a5c71c22.tar.gz samba-f62eaeb1a5add34ee7353d0d95db3c84a5c71c22.tar.bz2 samba-f62eaeb1a5add34ee7353d0d95db3c84a5c71c22.zip | |
regenerate
(This used to be commit 75a8a906e8031b50e6583f2e0354073a8aa7f5f3)
Diffstat (limited to 'docs/htmldocs/locking.html')
| -rw-r--r-- | docs/htmldocs/locking.html | 657 |
1 files changed, 0 insertions, 657 deletions
diff --git a/docs/htmldocs/locking.html b/docs/htmldocs/locking.html deleted file mode 100644 index 6214254ce0..0000000000 --- a/docs/htmldocs/locking.html +++ /dev/null @@ -1,657 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> -<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 14. File and Record Locking</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.60.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="AccessControls.html" title="Chapter 13. File, Directory and Share Access Controls"><link rel="next" href="securing-samba.html" title="Chapter 15. Securing Samba"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 14. File and Record Locking</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="AccessControls.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="securing-samba.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="locking"></a>Chapter 14. File and Record Locking</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jelmer</span> <span class="othername">R.</span> <span class="surname">Vernooij</span></h3><div class="affiliation"><span class="orgname">The Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jelmer@samba.org">jelmer@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Eric</span> <span class="surname">Roseme</span></h3><div class="affiliation"><span class="orgname">HP Oplocks Usage Recommendations Whitepaper<br></span><div class="address"><p><tt class="email"><<a href="mailto:eric.roseme@hp.com">eric.roseme@hp.com</a>></tt></p></div></div></div></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="locking.html#id2926847">Features and Benefits</a></dt><dt><a href="locking.html#id2926902">Discussion</a></dt><dd><dl><dt><a href="locking.html#id2927033">Opportunistic Locking Overview</a></dt></dl></dd><dt><a href="locking.html#id2925408">Samba Opportunistic Locking Control</a></dt><dd><dl><dt><a href="locking.html#id2925517">Example Configuration</a></dt></dl></dd><dt><a href="locking.html#id2925776">MS Windows Opportunistic Locking and Caching Controls</a></dt><dd><dl><dt><a href="locking.html#id2928213">Workstation Service Entries</a></dt><dt><a href="locking.html#id2928240">Server Service Entries</a></dt></dl></dd><dt><a href="locking.html#id2928320">Persistent Data Corruption</a></dt><dt><a href="locking.html#id2928350">Common Errors</a></dt><dd><dl><dt><a href="locking.html#id2928423">locking.tdb error messages</a></dt></dl></dd><dt><a href="locking.html#id2928454">Additional Reading</a></dt></dl></div><p> -One area which causes trouble for many network administrators is locking. -The extent of the problem is readily evident from searches over the internet. -</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2926847"></a>Features and Benefits</h2></div></div><div></div></div><p> -Samba provides all the same locking semantics that MS Windows clients expect -and that MS Windows NT4 / 200x servers provide also. -</p><p> -The term <span class="emphasis"><em>locking</em></span> has exceptionally broad meaning and covers -a range of functions that are all categorized under this one term. -</p><p> -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. -</p><p> -The MS Windows network administrator needs to be aware that file and record -locking semantics (behaviour) can be controlled either in Samba or by way of registry -settings on the MS Windows client. -</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> -Sometimes it is necessary to disable locking control settings BOTH on the Samba -server as well as on each MS Windows client! -</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2926902"></a>Discussion</h2></div></div><div></div></div><p> -There are two types of locking which need to be performed by a SMB server. -The first is <span class="emphasis"><em>record locking</em></span> which allows a client to lock -a range of bytes in a open file. The second is the <span class="emphasis"><em>deny modes</em></span> -that are specified when a file is open. -</p><p> -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 can not be fully correct due to 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. -</p><p> -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 0-2^31, Samba hands this request down to the Unix system. -All other locks can not be seen by unix anyway. -</p><p> -Strictly a 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 <b class="command">rpc.lockd</b>. It is also almost always unnecessary as clients are supposed to -independently make locking calls before reads and writes anyway if locking is -important to them. By default Samba only makes locking calls when explicitly asked -to by a client, but if you set <i class="parameter"><tt>strict locking = yes</tt></i> then it -will make lock checking calls on every read and write. -</p><p> -You can also disable byte range locking completely using <i class="parameter"><tt>locking = no</tt></i>. -This is useful for those shares that don't support locking or don't need it -(such as cdroms). In this case Samba fakes the return codes of locking calls to -tell clients that everything is OK. -</p><p> -The second class of locking is the <i class="parameter"><tt>deny modes</tt></i>. 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 -<tt class="constant">DENY_NONE</tt>, <tt class="constant">DENY_READ</tt>, -<tt class="constant">DENY_WRITE</tt> or <tt class="constant">DENY_ALL</tt>. There are also special compatibility -modes called <tt class="constant">DENY_FCB</tt> and <tt class="constant">DENY_DOS</tt>. -</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2927033"></a>Opportunistic Locking Overview</h3></div></div><div></div></div><p> -Opportunistic locking (Oplocks) is invoked by the Windows file system -(as opposed to an API) via registry entries (on the server AND 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 which allows: -</p><div class="variablelist"><dl><dt><span class="term">Read-ahead:</span></dt><dd><p> - The client reads the local copy of the file, eliminating network latency - </p></dd><dt><span class="term">Write caching:</span></dt><dd><p> - The client writes to the local copy of the file, eliminating network latency - </p></dd><dt><span class="term">Lock caching:</span></dt><dd><p> - The client caches application locks locally, eliminating network latency - </p></dd></dl></div><p> -The performance enhancement of oplocks is due to the opportunity of -exclusive access to the file - even if it is opened with deny-none - -because Windows monitors the file's status for concurrent access from -other processes. -</p><div class="variablelist"><p class="title"><b>Windows defines 4 kinds of Oplocks:</b></p><dl><dt><span class="term">Level1 Oplock:</span></dt><dd><p> - 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. - </p><p> - If a second process attempts to open the file, the open - is deferred while the redirector "breaks" 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. - </p></dd><dt><span class="term">Level2 Oplock:</span></dt><dd><p> - 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. - </p></dd><dt><span class="term">Filter Oplock:</span></dt><dd><p> - Does not allow write or delete file access - </p></dd><dt><span class="term">Batch Oplock:</span></dt><dd><p> - Manipulates file openings and closings - allows caching - of file attributes - </p></dd></dl></div><p> -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. -</p><p> -<span class="emphasis"><em>Opportunistic Locking</em></span> 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. -</p><p> -The actual decision that a user or administrator should consider is -whether it is sensible to share amongst 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 -"opportunistic locking" should be treated as a toggle for client-side -caching. Turn it "ON" when client-side caching is desirable and -reliable. Turn it "OFF" when client-side caching is redundant, -unreliable, or counter-productive. -</p><p> -Opportunistic locking is by default set to "on" 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. -</p><p> -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. -</p><p> -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. -n 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. -</p><p> -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 -- as in a file server failover - 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 - at worst, abort and -require restarting. -</p><p> -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. -</p><p> -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. -</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925067"></a>Exclusively Accessed Shares</h4></div></div><div></div></div><p> -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. -</p><p> -Home directories are the most obvious examples of where the performance -benefit of opportunistic locking can be safely realized. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925092"></a>Multiple-Accessed Shares or Files</h4></div></div><div></div></div><p> -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. -</p><p> -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. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925121"></a>Unix or NFS Client Accessed Files</h4></div></div><div></div></div><p> -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. -</p><p> -If files are shared between Windows clients, and either local Unix -or NFS users, then turn opportunistic locking off. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925147"></a>Slow and/or Unreliable Networks</h4></div></div><div></div></div><p> -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 very 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. -</p><p> -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. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925180"></a>Multi-User Databases</h4></div></div><div></div></div><p> -Multi-user databases clearly pose a risk due to their very nature - -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. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925202"></a>PDM Data Shares</h4></div></div><div></div></div><p> -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. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925229"></a>Beware of Force User</h4></div></div><div></div></div><p> -Samba includes an <tt class="filename">smb.conf</tt> parameter called <i class="parameter"><tt>force user</tt></i> 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. -</p><p> -Avoid the combination of the following: -</p><div class="itemizedlist"><ul type="disc"><li><p> - <i class="parameter"><tt>force user</tt></i> in the <tt class="filename">smb.conf</tt> share configuration. - </p></li><li><p> - Slow or unreliable networks - </p></li><li><p> - Opportunistic Locking Enabled - </p></li></ul></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925306"></a>Advanced Samba Opportunistic Locking Parameters</h4></div></div><div></div></div><p> -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: -<i class="parameter"><tt>oplock break wait time</tt></i>, -<i class="parameter"><tt>oplock contention limit</tt></i>. -</p><p> -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 "DO NOT CHANGE THIS -PARAMETER UNLESS YOU HAVE READ AND UNDERSTOOD THE SAMBA OPLOCK CODE." -This is good advice. -</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925349"></a>Mission Critical High Availability</h4></div></div><div></div></div><p> -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. -</p><p> -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 -- as in a file server failover - 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 - at worst, abort and -require restarting. -</p><p> -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. -</p><p> -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. -</p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2925408"></a>Samba Opportunistic Locking Control</h2></div></div><div></div></div><p> -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 defacto 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. -</p><p> -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. -</p><p> -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 synchronise the file back to the server. -This can give significant performance gains in some cases; some programs insist on -synchronising the contents of the entire file back to the server for a single change. -</p><p> -Level1 Oplocks (aka just plain "oplocks") is another term for opportunistic locking. -</p><p> -Level2 Oplocks provides opportunistic locking for a file that will be treated as -<span class="emphasis"><em>read only</em></span>. 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. -</p><p> -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 under lying OS, SGI IRIX and Linux are the only two OS's that are -oplock aware at this time. -</p><p> -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 synchronisation 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 very badly to oplocks. If in doubt, -disable oplocks and tune your system from that point. -</p><p> -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. -</p><p> -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. -</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2925517"></a>Example Configuration</h3></div></div><div></div></div><p> -In the following we examine two distinct aspects of Samba locking controls. -</p><div xmlns:ns38="" class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925530"></a>Disabling Oplocks</h4></div></div><div></div></div><p> -You can disable oplocks on a per-share basis with the following: -</p><ns38:p> -</ns38:p><pre class="programlisting"> -[acctdata] - oplocks = False - level2 oplocks = False -</pre><ns38:p> -</ns38:p><p> -The default oplock type is Level1. Level2 Oplocks are enabled on a per-share basis -in the <tt class="filename">smb.conf</tt> file. -</p><p> -Alternately, you could disable oplocks on a per-file basis within the share: -</p><ns38:p> -</ns38:p><pre class="programlisting"> - veto oplock files = /*.mdb/*.MDB/*.dbf/*.DBF/ -</pre><ns38:p> -</ns38:p><p> -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. -</p></div><div xmlns:ns39="" class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2925592"></a>Disabling Kernel OpLocks</h4></div></div><div></div></div><p> -Kernel OpLocks is an <tt class="filename">smb.conf</tt> 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 <tt class="filename">smb.conf</tt> file. -</p><ns39:p> -</ns39:p><pre class="programlisting"> -[global] -kernel oplocks = yes -</pre><ns39:p> -The default is "no". -</ns39:p><p> -Veto OpLocks is an <tt class="filename">smb.conf</tt> 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 -<tt class="filename">smb.conf</tt> file: -</p><ns39:p> -</ns39:p><pre class="programlisting"><font color="red"><title>Example Veto OpLock Settings</title></font> -[global] - veto oplock files = /filename.htm/*.txt/ - -[share_name] - veto oplock files = /*.exe/filename.ext/ -</pre><ns39:p> -</ns39:p><p> -<span class="emphasis"><em>Oplock break wait time</em></span> is an <tt class="filename">smb.conf</tt> parameter that adjusts the time -interval for Samba to reply to an oplock break request. Samba -recommends "DO NOT CHANGE THIS PARAMETER UNLESS YOU HAVE READ AND -UNDERSTOOD THE SAMBA OPLOCK CODE." Oplock Break Wait Time can only be -configured globally in the <tt class="filename">smb.conf</tt> file: -</p><ns39:p> -</ns39:p><pre class="programlisting"> -[global] - oplock break wait time = 0 (default) -</pre><ns39:p> -</ns39:p><p> -<span class="emphasis"><em>Oplock break contention limit</em></span> is an <tt class="filename">smb.conf</tt> 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 "DO NOT CHANGE THIS PARAMETER UNLESS YOU -HAVE READ AND UNDERSTOOD THE SAMBA OPLOCK CODE." Oplock Break -Contention Limit can be enable on a per-share basis, or globally for -the entire server, in the <tt class="filename">smb.conf</tt> file: -</p><ns39:p> -</ns39:p><pre class="programlisting"> -[global] - oplock break contention limit = 2 (default) - -[share_name] - oplock break contention limit = 2 (default) -</pre><ns39:p> -</ns39:p></div></div></div><div xmlns:ns40="" class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2925776"></a>MS Windows Opportunistic Locking and Caching Controls</h2></div></div><div></div></div><p> -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 <span class="emphasis"><em>Opportunistic Locking</em></span>. 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 <span class="errorname">Access Denied</span> - error message being displayed during network operations. -</p><p> -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. -</p><p> -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. -</p><p> -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. -</p><p> -You can verify (or 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. -</p><p> -The location of the client registry entry for opportunistic locking has changed in -Windows 2000 from the earlier location in Microsoft Windows NT. -</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> -Windows 2000 will still respect the EnableOplocks registry value used to disable oplocks -in earlier versions of Windows. -</p></div><p> -You can also deny the granting of opportunistic locks by changing the following registry entries: -</p><ns40:p> -</ns40:p><pre class="programlisting"> - HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\MRXSmb\Parameters\ - - OplocksDisabled REG_DWORD 0 or 1 - Default: 0 (not disabled) -</pre><ns40:p> -</ns40:p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> -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. -</p></div><ns40:p> -</ns40:p><pre class="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) -</pre><ns40:p> -</ns40:p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> -The EnableOplocks value configures Windows-based servers (including Workstations sharing -files) to allow or deny opportunistic locks on local files. -</p></div><p> -To force closure of open oplocks on close or program exit EnableOpLockForceClose must be set to 1. -</p><p> -An illustration of how level II oplocks work: -</p><div class="itemizedlist"><ul type="disc"><li><p> - Station 1 opens the file, requesting oplock. - </p></li><li><p> - Since no other station has the file open, the server grants station 1 exclusive oplock. - </p></li><li><p> - Station 2 opens the file, requesting oplock. - </p></li><li><p> - Since station 1 has not yet written to the file, the server asks station 1 to Break - to Level II Oplock. - </p></li><li><p> - Station 1 complies by flushing locally buffered lock information to the server. - </p></li><li><p> - Station 1 informs the server that it has Broken to Level II Oplock (alternatively, - station 1 could have closed the file). - </p></li><li><p> - The server responds to station 2's open request, granting it level II oplock. - Other stations can likewise open the file and obtain level II oplock. - </p></li><li><p> - Station 2 (or any station that has the file open) sends a write request SMB. - The server returns the write response. - </p></li><li><p> - 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. - </p></li></ul></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928213"></a>Workstation Service Entries</h3></div></div><div></div></div><pre class="programlisting"> - \HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\LanmanWorkstation\Parameters - - UseOpportunisticLocking REG_DWORD 0 or 1 - Default: 1 (true) -</pre><p> -Indicates whether the redirector should use opportunistic-locking (oplock) performance -enhancement. This parameter should be disabled only to isolate problems. -</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928240"></a>Server Service Entries</h3></div></div><div></div></div><pre class="programlisting"> - \HKEY_LOCAL_MACHINE\System\ - CurrentControlSet\Services\LanmanServer\Parameters - - EnableOplocks REG_DWORD 0 or 1 - Default: 1 (true) -</pre><p> -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. -</p><pre class="programlisting"> - MinLinkThroughput REG_DWORD 0 to infinite bytes per second - Default: 0 -</pre><p> -Specifies the minimum link throughput allowed by the server before it disables -raw and opportunistic locks for this connection. -</p><pre class="programlisting"> - MaxLinkDelay REG_DWORD 0 to 100,000 seconds - Default: 60 -</pre><p> -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. -</p><pre class="programlisting"> - OplockBreakWait REG_DWORD 10 to 180 seconds - Default: 35 -</pre><p> -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. -</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928320"></a>Persistent Data Corruption</h2></div></div><div></div></div><p> -If you have applied all of the settings discussed in this paper but data corruption problems -and other symptoms persist, here are some additional things to check out: -</p><p> -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. -</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928350"></a>Common Errors</h2></div></div><div></div></div><p> -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. -</p><p> -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: -</p><div class="itemizedlist"><ul type="disc"><li><p> - Incorrect configuration of opportunistic locking (incompatible with the application - being used. This is a VERY 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. - </p></li><li><p> - Defective network cards, cables, or HUBs / Switched. This is generally a more - prevalent factor with low cost networking hardware, though occasionally there - have been problems with incompatibilities in more up market hardware also. - </p></li><li><p> - There have been some random reports of samba log files being written over data - files. This has been reported by very few sites (about 5 in the past 3 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 https://bugzilla.samba.org without delay. Make sure that you give as much - information as you possibly can to help isolate the cause and to allow reproduction - of the problem (an essential step in problem isolation and correction). - </p></li></ul></div><div xmlns:ns41="" class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928423"></a>locking.tdb error messages</h3></div></div><div></div></div><ns41:p> - </ns41:p><pre class="screen"> - > We are seeing lots of errors in the samba logs like: - > - > tdb(/usr/local/samba_2.2.7/var/locks/locking.tdb): rec_read bad magic - > 0x4d6f4b61 at offset=36116 - > - > What do these mean? - </pre><ns41:p> - </ns41:p><p> - Corrupted tdb. Stop all instances of smbd, delete locking.tdb, restart smbd. - </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928454"></a>Additional Reading</h2></div></div><div></div></div><p> -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. -</p><p> -Section of the Microsoft MSDN Library on opportunistic locking: -</p><p> -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. -<a href="http://msdn.microsoft.com/library/en-us/fileio/storage_5yk3.asp" target="_top">http://msdn.microsoft.com/library/en-us/fileio/storage_5yk3.asp</a> -</p><p> -Microsoft Knowledge Base Article Q224992 "Maintaining Transactional Integrity with OPLOCKS", -Microsoft Corporation, April 1999, <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q224992" target="_top">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q224992</a>. -</p><p> -Microsoft Knowledge Base Article Q296264 "Configuring Opportunistic Locking in Windows 2000", -Microsoft Corporation, April 2001, <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q296264" target="_top">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q296264</a>. -</p><p> -Microsoft Knowledge Base Article Q129202 "PC Ext: Explanation of Opportunistic Locking on Windows NT", - Microsoft Corporation, April 1995, <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q129202" target="_top">http://support.microsoft.com/default.aspx?scid=kb;en-us;Q129202</a>. -</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="AccessControls.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="securing-samba.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 13. File, Directory and Share Access Controls </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 15. Securing Samba</td></tr></table></div></body></html> |