Hi Pavel,

  first of all, I am running a single node in my machine... This should 
not be a problem.

> The way how it should work is that xrootd on redirector node pass its 
> prepare request to olbd and olbd keeps track of servers which are able 
> to prepare files (you are saying it by olb.prep directive). When the 
> olbd on redirector node chooses best node to serve prepare request, the 
> request is passed trough the olbd to that server.
> The chosen server will initiate add command on its forked olb prep 
> command and the particular prep command should add this file into its 
> queue. (this is the /tmp/pre_stage.queue.0)

  Problem #1 is that I don't see this queue file. A new file gets 
created in /tmp/prestage_log/anon/. This new file contains the filename 
I am willing to prestage.

> Now it is a time to bring files from your tape system. So, the way how 
> it is done is that you need to run on each dataserver executable called 
> mps_PreStage. This executable needs to be started along with the xrootd 
> and olbd as a separate process. This executable is looking into this 
> /tmp/pres_stage.queue.0  and it is grabbing files one by one and 
> initiate this command in you configuration mps.pstg.pstgcmd.
> Don't forget that you need to start mps_PreStage command with -c option 
> to pass the configuration file.

  Urgh, shall I launch mps_PreStage manually? This looks strange to me, 
I did not understand that. Anyway I launched it and I am keeping it 
running. For now, it generates no output.

> Could you please enable
> olb.trace all debug
> odc.trace all debug
> in your configuration files ? So, we can see if the request is passed to 
> olb ?

  Done, but no change in the logfile with respect to before.

> Thanks
> I hope I didn't confuse you

  Not at all, I owe a beer to you, two if I succeed!