How hard is unRAID to use if I don know Linux?
Not hard at all. Although the unRAID server software is based on a slimmed-down Linux, it is managed almost entirely from your web browser, typically on a Windows or Mac computer. Some users are happy with that, but many want to take advantage of the many tweaks and addons for unRAID, and these usually require a little hands-on work. But they are completely optional, and are generally accompanied with lots of help and instructions, and there is a very helpful user community. Many users find this makes for a good (but limited) introduction to Linux, at your own pace. See also this thread, especially this post, for more comments.
