My first question is will this have an effect on exiting data in existing pool nodes? The DPM mysql server is already hosted on a separate machine, which is not changing.
No - you should be fine - the main thing to ensure is that the database is safe. (But of course I would also make a copy of everything else.)
Just point at the mysql server with your new head node and that should be fine.
Secondly, the existing head node has some old RAIDs hanging directly off it, so I would like to convert it into a normal pool node. How should this be done? My plan so far consists of 1) draining the RAIDS onto an existing pool node 2) installing the new head node 3) configuring the old head node to be a pool node 4) drain the files back. Are there any obvious pitfalls here?
Sounds good - if you have the free space. You could probably get away without draining the machine (or even reinstalling it). The head node should have all the services required to be a pool node. If you just make the new head node aware of the filesystems on their (in YAIM or dpm-addfs) and trust it
http://www.gridpp.ac.uk/wiki/DPM_Install#Ensure_nodes_trust_each_other. I would stop all head node services on the old head node though if you don't reinstall it. I might be tempted though to set up the new node in parallel and make sure it works and then move everything across (for ATLAS etc. as below) then switch off the old node to see that nothing breaks and then probably reinstall it from scratch as a disk node and maybe change the hostname - to try and avoid a confusing situation if something somewhere is pointing at the old node and so does something strange.
Finally, what are the implications for changing the SE name from ATLAS' point of view? Presumeably the ToA will have to change? Who would have to know about this?
Yes - I think Manchester did this recently so maybe should be able to offer some advice. If you want both "sites" in for a while then you can ask for another site to be defined in ToA - it seems people put _PPSDISK at the end of the site name for the new test site. Or you could just do it in one step if it just a hostname change. You can either send a DDM Savannah directly within Atlas or contact
[log in to unmask] to do it for you. For other VOs etc, you will also want to change the publishing on your site BDII and the CE. You will also need an entry for the new node in the GOCDB.