[OSM-dev] Tiles at home - future disk ideas

[OJW]

There were many suggestions on wiki for spreading the load across two disks:

http://wiki.openstreetmap.org/index.php/Tiles%40home/Dev/Website/

When evaluating those ideas, remember that Stuff takes a long time on dev.  
Rearranging data takes a long time (133GB of images while the CPU is already 
in iowait). Rearranging databases takes a long time (27 million rows, while 
MySQL is already being written-to 300 times per second). Searching for 
particular types of image, bulk-copying database rows around, even deleting a 
particular set of images, all take a fair while to complete. 

My favourite suggestion was the virtual filesystem spanning multiple disks, 
since it means that tiles can be served using mod-rewrite, and doesn't 
require adding complexity to the server code.  (schemes with "odd tiles on 
disk 2" and similar sound interesting, but they need implementing as 
mod-rewrite rules, which is harder than simply suggesting the strategy)

So a single filesystem is interesting, but will need a bit of help from 
filesystem-admin type people.  Has anyone tested performance of such a system 
compared to regular disks?  What do we do with existing files while the disk 
is being generated? How easy will it be to add the 3rd and 4th disks?  I'm 
happy to use such a system if it appears on dev, but implementing it is 
something for the server admins.