Sliding Rails for 3100

Sounds like it does. In The Specifications Section of the Definitive Guide to the ReadyNAS 3100, there is listed rackmount sliding rails under optional spare parts.

However note what Boba Fett said (http://www.readynas.com/forum/viewtopic.php?p=244797#p244797):

Boba Fett wrote:
The 3100 rack sliding rail kit is included in the system package. are you looking for extra as spare?

Thanks for the reply from the product description it sounds like an optional product not part of the package.. good to know they come with it..

Kevin

"Optional spare part" i.e. spare part you can purchase to replace what is included in the package if it fails. Some people like to have a spare part on hand to minimise downtime. Sliding rails are not a component that's likely to fail so unless you're managing a huge number of units you're unlikely to want a spare.