Disclaimer: Microsoft ended support for WHS 2011 on April 12, 2016. The software is considered "abandonware." However, you should not pirate software. The only legal ways to obtain the ISO today are:
The Short Answer: Only for legacy hardware or offline homelabs.
Tech resellers like CDW or Insight occasionally retain download links for purchased software. If you have a valid product key, you may request a replacement ISO.
The official ISO for WHS 2011 is a 4.1 GB downloadable disk image containing:
Windows Home Server 2011, code-named "Vail," is a server operating system by Microsoft, designed for home use. It was released on April 6, 2011. The software allows users to share files, stream media, and have automatic backup and remote access to PCs in the home network.
WHS 2011 differs from standard Windows because it uses a "Dashboard" for management rather than the standard Server Manager tools.
To streamline your search for the Microsoft Windows Home Server 2011 X64 ISO: