write behind caching

[Chris Dillon]

Moved to freebsd-questions, which is more appropriate...

On Thu, 18 Sep 2003, Mark Bojara wrote:

> One of our clients is running a FreeBSD 4.8 server with Samba for
> his Windows based financial system. He is having problems that the
> index files get corrupt. He phoned support for the financial system
> they told him he must disable "Write behind caching" on the server,
> However this is for a M$ server. Is there something equivilent for
> FreeBSD?

This is almost always due to an application programming error, but you
can't tell the developers that, and instead of fixing their problem,
the developers nearly always tell you to turn off "write caching".
What they really mean to say is "opportunistic locking".  Turn that
off in Samba and things will work smoothly, though much slower.  This
has _ABSOLUTELY NOTHING_ to do with any write caching performed by the
server OS or storage subsystem, nor with their "sync" behaviours.
This is entirely client-side caching (though server-orchestrated)
and has only to do with SMB file locking and a _client_ performing
write caching on a network file while other clients are performing
read caching on the same file, and the whole ballet of cache flushings
don't happen when they're supposed to.  Or something like that.

Before you turn off opportunistic locking, though, if the application
uses the Microsoft Data Access Components (MDAC) and/or Jet for its
database backend, download the latest MDAC and/or Jet release from
Microsoft's web site and install it on _every_ workstation.  That kind
of thing is ideal to put in a login script while using the silent
install option.  I believe the latest MDAC release is 2.8, and the
latest Jet is 4.0 SP7.  It will never hurt to install both, even if it
turns out your application uses neither.


-- 
 Chris Dillon - cdillon(at)wolves.k12.mo.us
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