[PVFS-users] PVFS mechanics

[Brian Jones]

Hi all, 

I'm actually just trying to make sure I really understand how PVFS
really *works*, because the documentation (though there's plenty of
it) is rather vague with regard to the conversation that takes place
between the players involved. I'm writing an article on PVFS, partly as
an exercise to make sure I understand it myself, and want to make sure I
have all my ducks in a row. I'm running pvfs as supplied with ROCKS
3.3.0 on dual 933 PIII nodes. 

Best I can tell from doing lots of tcpdumps, when a pvfs client wants to
copy a file to a pvfs directory, the following things happen:

1. The client contacts the metadata server, presumably to request
service, possibly to say it wants to either read or write, but for all I
know it may just be a ping. Clarification?

2. The metadata server responds and says something akin to "whaddya
got?"

3. The client tells the metadata server that it wants to copy a file in,
of a particular size, having particular ownership attributes, etc.

4. The metadata server records this information, and tells the client
where to send the actual data chunks that make up this file. 

5. The client sends the data chunks off to the designated IODs, who send
back an "ack" saying they got the data. 

6. The client sends some form of confirmation of these events to the
metadata server, so it knows for sure where everything is in the event
that the file later needs to be accessed/deleted/whatever. 

Of course, this is all from the client end of the conversation. If
anyone wants to add/correct/clarify anything, PLEASE do so. 

Thanks,
brian.