[OpenAFS] delayed write failures with windows client 1.4.0096

[Jeffrey Altman]

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Rodney M Dyer wrote:
> At 10:54 AM 4/11/2006, ted creedon wrote:
>> There are delayed write failures when using MS Office products (Excel,
>> MS Access) and other hangups requiring a reboot.
> 
> I've also seen these failures from time to time (I'm on 1.4.0 Windows
> client).  Just a completely anecdotal observation seems to suggest that
> this occurs more often when the cache is full, but I cannot verify
> that.  I have the issue also with Visual Studio projects that I work on
> out of AFS from time to time.
> 
> I haven't sat down and spent the time to acquire data for debugging. 
> It's just easier to ignore the problem.  The problem hasn't impacted me
> so far.

The delayed write errors are reported when the AFS cache manager is
unable to perform the requested operation before the Windows SMB/CIFS
client times out.  In 1.4.1-rc6 this happened quite frequently because
there was a bug that resulted in the file servers being marked as "down"
even when they were "up".

As mentioned briefly in the release notes, it is possible to increase
the timeout period of the Windows SMB/CIFS client by setting a registry
value.  The SMB/CIFS client by default uses a 45 second timeout value
that is adjusted based upon the speed of the network and the average RTT
to the server.  When the SMB/CIFS client is communicating with the AFS
Cache Manager it suffers from two problems.  First, the loopback
interface does not advertise a network bandwidth.  Second, most
operations to the AFS Cache Manager when working out of the cache occur
at disk speed.  When a request has to be sent to the file server to
fulfill an operation it takes place at network speed and if there is a
delay because of network congestion or the file server is busy (or
perhaps because the file server must break callbacks to the client
before it will allow a new rx connection to be created) then the
actual RTT will far exceed the average RTT.  In this situation the
Windows SMB/CIFS client will timeout and drop the connection to the
AFS Cache Manager.  One side effect is that you can obtain delayed
write errors when writing.

These problems will go away when AFS Cache Manager is accessed via
the Installable File System.

Jeffrey Altman

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