In a blog post in January, Tor executive director Andrew Lewman wrote that one of the five Iranian ISPs is now blocking publicly-known Tor nodes, even when that connection is encrypted.
Decoupling refresh cycles lets data center customers purchase server compute nodes, which are essentially very small motherboards (processor, system memory, boot environment, management, and connection to a local network fabric), separately from rack-level data center network interfaces (1GbE and 10GbE), separately from mass storage (hard disks and solid-state drives).