An external USB DVD Writer is connected to a client device. USB drive redirection is set up and a device rule added for the DVD Writer in Studio and Receiver policies. Client device mapping is disabled to prevent the DVD writer being mapped by Citrix drive mapping virtual channel. However the device appears in desktop viewer it is not possible to redirect it as the "Redirect" button is greyed out.

This is by design for the Windows Server versions 2008r2 and 2012r2 when used within Citrix. 

• USB mass storage devices cannot be mapped/redirected to an ICA session on a multi-user server 2008r2 and 2012r2 OS VDA. The external USB DVD Writer, as seen above, is a mass storage device. It is however possible to redirect the same device to a VDA with a desktop OS since the desktop OS is single-user.
• Using Server 2016 will allow the device to redirect without an issue