scale up to many nodes

[zooko]

I updated The UseCases Page to reflect that someone might want to run a managed Tahoe grid comprising one thousand nodes. (If each node has a single 1 TB hard drive, that's a 1 PB grid. Obviously there are lots of other options, such as each node having six 1 TB hard drives in a RAID-6 configuration, resulting in 4 usable TB per node or a 4 PB grid.)

Anyway, we expect that the current Tahoe grid would have problems handling more simultaneously connected nodes. One known problem is that pyOpenSSL uses almost 1 MB of RAM per SSL connection. (See also #11.)

This ticket can be closed when Tahoe is demonstrated to handle one thousand simultaneously connected nodes smoothly.