Add me to the list of people who had GLACIALLY slow SMB/CIFS/network file transfer performance between Server 2012 and XP or 7 clients – no idea if it would be any better with a Windows 8 client, but it was TERRIBLE (read: less than 500 KB/sec on gigabit network with solid state storage) file server performance and XP clients.
Also add me to the list of people for whom disabling mandatory SMB signing did the trick to cure the problem.
Open up Group Policy Editor, and right-click-and-edit Default Domain Controller Policy. Go to Computer Configuration/Policies/Windows Settings/Security Settings/Local Policies/Security Options, and set Domain member: Digitally encrypt or sign secure channel data (always) and Microsoft network server: Digitally sign communications (always) to Disabled.
In theory, gpupdate /force should get the job done, but in practice I had to reboot my Server 2012 instance to make it take effect. Once I’d done so, the difference in speed was extremely obvious – even folder listings were visibly faster, and copying a 9MB file from a share to a client desktop went from taking 20+ seconds to being instantaneous, as it bloody well should be.
Worth noting: this shouldn’t be a problem on a non-domain-controller 2012 server, as you can see from the location of the GPs I had to edit. Also worth noting: these settings aren’t set correctly on Windows Server Essentials 2012 either, despite the fact that WSE is always both a domain controller and a fileserver. Way to QA your products, MS… sigh.