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!==
!== File-Cacheing.txt for Samba release 2.0.7 26 Apr 2000
!==
Some people report problems with "cacheing" of data. Generally the bug report
goes like this:
- create a file on a unix box
- view the file on a PC via Samba
- change the file on the unix box
- look at the file again on the PC via Samba and the changes are not visible
The first thing to realise is that this is the expected behaviour! The SMB protocol
uses a thing called "opportunistic locking". This allows the client to "safely"
do client side cacheing of file data. The problem is that this cacheing is only
safe if all programs access the files via SMB. As soon as you access the data
via a non-SMB client then you will get data inconsistencies.
There are two solutions. Firstly, Samba has added a kernel level
interface that allows access from a UNIX client either via NFS
or a local process to notify Samba to 'break' the oplock, and
thus force the correct data to be seen. Currently the only UNIX
operating system that supports this interface is SGI IRIX 6.5.3f
and above. However, this interface is currently being discussed
for inclusion in both Linux and FreeBSD, and some of the other
UNIX vendors are also interested in supporting it.
The second solution is to disable oplocks in smb.conf for those shares
that need to be accessed simutaneously from unix and windows. See the
"oplocks" and "veto oplock files" options in smb.conf(5). Unfortunately
this will cause a speed penalty but with the non-kernel method this
cannot be avoided if up to date data is required for files accessed
from both Windows and UNIX.
Two more data points :
Samba-1.9.18 and later series supports oplocks.
Samba-1.9.17 series does NOT.
In addition, the following registry entries under MS Windows NT4 will
turn off oplocks on a client. WARNING !!!! This is *NOT* recommended
and will turn off oplocks for *all* servers aceessed from this client.
===================================================================================
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Paramete
rs]
"BufFilesDenyWrite"=dword:00000000
"BufNamedPipes"=dword:00000000
"UseOpportunisticLocking"=dword:00000000
"DormantFileLimit"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Paramete
rs\Linkage]
"UtilizeNtCaching"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Filesystem]
"Win95TruncateExtensions"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanManServer\Parameters]
"EnableOpLockForceClose"=dword:00000001
"EnableOpLocks"=dword:00000000
==================================================================================
The following registry entry does the same under Windows 9X also:
[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\VREDIR]
"DiscardCacheOnOpen"=string:00000001
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