What are Database/Datastores That Support On-Disk Multi-process Concurrency?

I'm looking to do random updates for up to 100 million "rows" of data and need to be able to access them in parallel processes (not threads). I'd prefer to use a solution that accessed the database from hard disk and not ram (unlike redis). Any options?

Some op开发者_JAVA技巧tions I've been looking into:

Tokyo Tyrant/Kyoto Tycoon: I'm not sure if they are on-disk like their cabinet brethren but they support concurrent access to a database from multiple processes.