From 83a17815a7689f1f6f7ca57161a0e804277c75f9 Mon Sep 17 00:00:00 2001 From: Jelmer Vernooij Date: Sun, 20 Jun 2004 12:43:16 +0000 Subject: New structure for the docs: - Same name for a doc everywhere (howto -> Samba-HOWTO-Collection, etc) - Shorter and more clearly structured Makefile - Make it possible to change the paths for the images (This used to be commit 96f6c05f25acc8a9bb1977b8bd5cc97ce511b6b1) --- docs/Samba-HOWTO-Collection/locking.xml | 1073 +++++++++++++++++++++++++++++++ 1 file changed, 1073 insertions(+) create mode 100644 docs/Samba-HOWTO-Collection/locking.xml (limited to 'docs/Samba-HOWTO-Collection/locking.xml') diff --git a/docs/Samba-HOWTO-Collection/locking.xml b/docs/Samba-HOWTO-Collection/locking.xml new file mode 100644 index 0000000000..555efd37a8 --- /dev/null +++ b/docs/Samba-HOWTO-Collection/locking.xml @@ -0,0 +1,1073 @@ + + + + %global_entities; + +]> + + + + &author.jeremy; + &author.jelmer; + &author.jht; + &author.eroseme; + +File and Record Locking + + +One area that causes trouble for many network administrators is locking. +The extent of the problem is readily evident from searches over the Internet. + + + +Features and Benefits + + +Samba provides all the same locking semantics that MS Windows clients expect +and that MS Windows NT4/200x servers also provide. + + + +The term locking has exceptionally broad meaning and covers +a range of functions that are all categorized under this one term. + + + +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. + + + +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. + + + + +Sometimes it is necessary to disable locking control settings on both the Samba +server as well as on each MS Windows client! + + + + + + +Discussion + + +There are two types of locking that need to be performed by an SMB server. +The first is record locking that allows a client to lock +a range of bytes in a open file. The second is the deny modes +that are specified when a file is open. + + + +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. + + + +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. + + + +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 rpc.lockd. 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 strict lockingyes, it +will make lock checking calls on every read and write call. + + + +You can also disable byte range locking completely by using +lockingno. +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. + + + +The second class of locking is the deny modes. 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 +DENY_NONE, DENY_READ, +DENY_WRITE, or DENY_ALL. There are also special compatibility +modes called DENY_FCB and DENY_DOS. + + + +Opportunistic Locking Overview + + +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: + + + + Read-ahead: + + The client reads the local copy of the file, eliminating network latency. + + + + Write caching: + + The client writes to the local copy of the file, eliminating network latency. + + + + Lock caching: + + The client caches application locks locally, eliminating network latency. + + + + + +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. + + + +Windows defines 4 kinds of Oplocks: + + Level1 Oplock + + 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. + + + + 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. + + + + Level2 Oplock + + 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. + + + + Filter Oplock + + Does not allow write or delete file access. + + + + Batch Oplock + + Manipulates file openings and closings and allows caching + of file attributes. + + + + + +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. + + + +Opportunistic locking 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. + + + +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 +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. + + + +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. + + + +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. + + + +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. + + + +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. + + + +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. + + + +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. + + + +Exclusively Accessed Shares + + +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. + + + +Home directories are the most obvious examples of where the performance +benefit of opportunistic locking can be safely realized. + + + + + +Multiple-Accessed Shares or Files + + +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. + + + +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. + + + + + +UNIX or NFS Client-Accessed Files + + +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. + + + +If files are shared between Windows clients, and either local UNIX +or NFS users, turn opportunistic locking off. + + + + + +Slow and/or Unreliable Networks + + +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. + + + +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. + + + + + +Multi-User Databases + + +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. + + + + + +PDM Data Shares + + +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. + + + + + +Beware of Force User + + +Samba includes an &smb.conf; parameter called +force user 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. + + + +Avoid the combination of the following: + + + + + force user in the &smb.conf; share configuration. + + + + Slow or unreliable networks + + + + Opportunistic locking enabled + + + + + + +Advanced Samba Opportunistic Locking Parameters + + +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: +oplock break wait time, +oplock contention limit. + + + +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. + + + + + +Mission-Critical High-Availability + + +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. + + + +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. + + + +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. + + + +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. + + + + + + + +Samba Opportunistic Locking Control + + +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. + + + +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. + + + +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. + + + +Level1 Oplocks (also known as just plain oplocks) is another term for opportunistic locking. + + + +Level2 Oplocks provides opportunistic locking for a file that will be treated as +read only. 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. + + + +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. + + + +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. + + + +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. + + + +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. + + + +Example Configuration + + +In the following section we examine two distinct aspects of Samba locking controls. + + + +Disabling Oplocks + + +You can disable oplocks on a per-share basis with the following: + + + + +[acctdata] +oplocksFalse +level2 oplocksFalse + + + + +The default oplock type is Level1. Level2 oplocks are enabled on a per-share basis +in the &smb.conf; file. + + + +Alternately, you could disable oplocks on a per-file basis within the share: + + + + +veto oplock files/*.mdb/*.MDB/*.dbf/*.DBF/ + + + + +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. + + + + + +Disabling Kernel Oplocks + + +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. + + + + +kernel oplocksyes + +The default is no. + + + +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 . + + + + +Share with some files oplocked +[global] +veto oplock files/filename.htm/*.txt/ + +[share_name] +veto oplock files/*.exe/filename.ext/ + + + + +oplock break wait time is an &smb.conf; 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 &smb.conf; file as shown below. + + + + +oplock break wait time 0 (default) + + + + +Oplock break contention limit 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 +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 &smb.conf; file as shown in . + + + + + Configuration with oplock break contention limit +[global] +oplock break contention limit 2 (default) + +[share_name] +oplock break contention limit 2 (default) + + + + + + + + + +MS Windows Opportunistic Locking and Caching Controls + + +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 opportunistic locking. 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 Access Denied + error message being displayed during network operations. + + + +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. +Microsoft has documented this in Knowledge Base article 300216. + + + +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. + + + +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. + + + +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. + + + +The location of the client registry entry for opportunistic locking has changed in +Windows 2000 from the earlier location in Microsoft Windows NT. + + + +Windows 2000 will still respect the EnableOplocks registry value used to disable oplocks +in earlier versions of Windows. + + + +You can also deny the granting of opportunistic locks by changing the following registry entries: + + + + + HKEY_LOCAL_MACHINE\System\ + CurrentControlSet\Services\MRXSmb\Parameters\ + + OplocksDisabled REG_DWORD 0 or 1 + Default: 0 (not disabled) + + + + +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. + + + + + 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) + + + + +The EnableOplocks value configures Windows-based servers (including Workstations sharing +files) to allow or deny opportunistic locks on local files. + + + +To force closure of open oplocks on close or program exit, EnableOpLockForceClose must be set to 1. + + + +An illustration of how Level2 oplocks work: + + + + + Station 1 opens the file requesting oplock. + + + Since no other station has the file open, the server grants station 1 exclusive oplock. + + + Station 2 opens the file requesting oplock. + + + Since station 1 has not yet written to the file, the server asks station 1 to break + to Level2 oplock. + + + Station 1 complies by flushing locally buffered lock information to the server. + + + Station 1 informs the server that it has Broken to Level2 Oplock (alternately, + station 1 could have closed the file). + + + The server responds to station 2's open request, granting it Level2 oplock. + Other stations can likewise open the file and obtain Level2 oplock. + + + Station 2 (or any station that has the file open) sends a write request SMB. + The server returns the write response. + + + 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. + + + + +Workstation Service Entries + + + \HKEY_LOCAL_MACHINE\System\ + CurrentControlSet\Services\LanmanWorkstation\Parameters + + UseOpportunisticLocking REG_DWORD 0 or 1 + Default: 1 (true) + + + +This indicates whether the redirector should use opportunistic-locking (oplock) performance +enhancement. This parameter should be disabled only to isolate problems. + + + + +Server Service Entries + + + \HKEY_LOCAL_MACHINE\System\ + CurrentControlSet\Services\LanmanServer\Parameters + + EnableOplocks REG_DWORD 0 or 1 + Default: 1 (true) + + + +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. + + + + MinLinkThroughput REG_DWORD 0 to infinite bytes per second + Default: 0 + + + +This specifies the minimum link throughput allowed by the server before it disables +raw and opportunistic locks for this connection. + + + + MaxLinkDelay REG_DWORD 0 to 100,000 seconds + Default: 60 + + + +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. + + + + OplockBreakWait REG_DWORD 10 to 180 seconds + Default: 35 + + + +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. + + + + + + +Persistent Data Corruption + + +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. + + + +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. + + + + + +Common Errors + + +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. + + + +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: + + + + + 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. + + + + 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. + + + + 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 Bugzilla 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). + + + + + locking.tdb Error Messages + + + + 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? + + + + + This error indicated a corrupted tdb. Stop all instances of smbd, delete locking.tdb, and restart smbd. + + + + + + Problems Saving Files in MS Office on Windows XP + + This is a bug in Windows XP. More information can be + found in Microsoft Knowledge Base article 812937. + + + + + + Long Delays Deleting Files Over Network with XP SP1 + + It sometimes takes approximately 35 seconds to delete files over the network after XP SP1 has been applied. + + This is a bug in Windows XP. More information can be found in + Microsoft Knowledge Base article 811492. + + + + + +Additional Reading + + +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. + + + +Section of the Microsoft MSDN Library on opportunistic locking: + + + +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. +http://msdn.microsoft.com/library/en-us/fileio/storage_5yk3.asp + + + + Microsoft Knowledge Base Article Q224992 Maintaining Transactional Integrity +with OPLOCKS, +Microsoft Corporation, April 1999, http://support.microsoft.com/default.aspx?scid=kb;en-us;Q224992. + + + +Microsoft Knowledge Base Article Q296264 Configuring Opportunistic Locking in Windows 2000, +Microsoft Corporation, April 2001, http://support.microsoft.com/default.aspx?scid=kb;en-us;Q296264. + + + +Microsoft Knowledge Base Article Q129202 PC Ext: Explanation of Opportunistic Locking on Windows NT, +Microsoft Corporation, April 1995, http://support.microsoft.com/default.aspx?scid=kb;en-us;Q129202. + + + + -- cgit