Hi Ewan,

On 19/08/08 13:06, Ewan MacMahon wrote:
> At the moment I'm not sure on how associations are made and kept 
> between files, paths, and tokens, nor the implications of the 
> Glasgow discovered DPM bug. 

Files are written to the DPM by the client. If the client specifies a 
space token (or a space token description) with the request, the file 
will be written "into" that token and XGB will be deducted from the 
available space in that token. There is no connection between the file 
path and the space which the file was written into.

That being said, ATLAS have chosen to encode the space token description 
in the file path. It remains to be seen if this is a good idea or not. 
In theory, all of this space token stuff gives VOs the abililty to do an 
srmChangeSpaceForFiles operation, where files in one space token are 
switched to another. This really only comes into play at the T1 where 
they may want to switch all files which are on tape to being in a space 
token which corresponds to all files being on disk and tape. Since T2s 
only have disk having the space token description name in the path 
shouldn't cause problems, but this is something to keep in mind.

The bug that was found at Glasgow was such that they tried to drain a 
filesystem. Since all of their space was already reserved in a series of 
ATLASXXXXX space token descriptions, according to DPM there was no free 
space left on the ATLAS pool. This resulted in all files going to the 
generalPool which still had available space that was not assigned to a 
space token. This means that although the files to be drained were 
already in a token, during the draining process DPM was not writing the 
files to the remaining space in that token.

If, for example, the generalPool did not exist (or only had access 
rights for non-ATLAS users) and Glasgow tried to drain the same 
filesystem, the DPM would complain that there was no free space to write 
the drained files into. The developers need to change things such that 
when a drain operation starts, the files are moved to another filesystem 
but stay in the same token.

Hope that explains things...

Cheers,
Greig

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