From 510064b14e8fddafe615f8c707023fcc3f84f094 Mon Sep 17 00:00:00 2001 From: Gerald Carter Date: Fri, 10 Oct 2003 16:21:39 +0000 Subject: removing docs from HEAD (This used to be commit 820903ef5a062b4b9824c33ee035c68a39c8eeb0) --- docs/docbook/projdoc/locking.xml | 1061 -------------------------------------- 1 file changed, 1061 deletions(-) delete mode 100644 docs/docbook/projdoc/locking.xml (limited to 'docs/docbook/projdoc/locking.xml') diff --git a/docs/docbook/projdoc/locking.xml b/docs/docbook/projdoc/locking.xml deleted file mode 100644 index 8bdb06ca8f..0000000000 --- a/docs/docbook/projdoc/locking.xml +++ /dev/null @@ -1,1061 +0,0 @@ - - - &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 -failover replacement will be available immediately to provide -continuous data availability. - - - -Windows client failover behavior is more at risk of application -interruption than other platforms because it is dependent upon an -established TCP transport connection. If the connection is interrupted -&smbmdash; as in a file server failover &smbmdash; a new session must be established. -It is rare for Windows client applications to be coded to recover -correctly from a transport connection loss, therefore, most applications -will experience some sort of interruption &smbmdash; at worst, abort and -require restarting. - - - -If a client session has been caching writes and reads locally due to -opportunistic locking, it is likely that the data will be lost when the -application restarts or recovers from the TCP interrupt. When the TCP -connection drops, the client state is lost. When the file server -recovers, an oplock break is not sent to the client. In this case, the -work from the prior session is lost. Observing this scenario with -oplocks disabled and with the client writing data to the file server -real-time, the failover will provide the data on disk as it -existed at the time of the disconnect. - - - -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 datastores. PDM applications manage multi-user -environments for critical data security and access. The typical PDM -environment is usually associated with sophisticated client design -applications that will load data locally as demanded. In addition, the -PDM application will usually monitor the data-state of each client. -In this case, client-side data caching is best left to the local -application and PDM server to negotiate and maintain. It is -appropriate to eliminate the client OS from any caching tasks, and the -server from any oplock management, by disabling opportunistic locking on -the share. - - - - - -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 -failover replacement will be available immediately to provide -continuous data availability. - - - -Windows client failover behavior is more at risk of application -interruption than other platforms because it is dependant upon an -established TCP transport connection. If the connection is interrupted -&smbmdash; as in a file server failover &smbmdash; a new session must be established. -It is rare for Windows client applications to be coded to recover -correctly from a transport connection loss, therefore, most applications -will experience some sort of interruption &smbmdash; at worst, abort and -require restarting. - - - -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. - - - -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. - - - -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 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. - - - - - -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