[OpenAFS] recovering corrupted save on file

David Bear David.Bear@asu.edu
Thu, 8 Jun 2006 17:29:16 -0700

On Wed, Jun 07, 2006 at 11:19:12PM -0400, Jeffrey Altman wrote:
> The cache does not store files it contains blocks.  There is no
> guarantee that a file will be entirely contained in the cache.
> You do not specify which OS you are using.  On Windows the cache
> file is simply a paging file for dedicated virtual memory.  Assuming
> the afsd_service.exe is shut down cleanly it would be possible to
> write code that could walk the contents of the cache to piece together
> the blocks of the file that exist.  However, no such tools currently
> exist.  The tool would have to be able to determine the cell, volume,
> vnode, and unique values for the file in order to find the correct
> stat cache entry and data buffers.

This is way to difficult. I wonder if there might be a better way. 

Since afs for windows uses a local smbserver, I wonder if that might
be hacked somehow to write temporary files to the local disk at the
same time that it passes the data off to the cach manager. It could
keep a files in a queue and push out the old like a LIFO queue...

> Jeffrey Altman
> David Bear wrote:
> > We have one room in one building that on occasion has some very
> > strange network disruption. It last about 8 minutes. When it clears
> > everything works fine.
> > 
> > The problem is that if someone has a file stored in an afs server open
> > on their client, AND they perform a save when the network has its
> > tantrum, the file is corrupted; either truncated to 0 bytes or filled
> > with garbage.
> > 
> > Is there any possible way to recover a file like this from the local
> > cache manager? I assume the local machine would commit some form of
> > the file to the local disk -- stored by the cache manager and then
> > actual write to the network would happen later. 
> > 
> > Of course we are trying to troubleshoot the network -- but at this
> > university that's not something that happens very fast... especially
> > when the problem is only intermittent.

David Bear
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