Microsoft launched KB3194721 (for SqlServer 2012) and KB3194718 (for SqlServer 2014) this month though WSUS channel. If you choose to deploy them though WSUS, just as I did, you may face a bug on a cluster based SqlServer.
On the server with SqlServer installed as cluster, these patches just act as cancelled or failed. For digging the problem, I download the package from Microsoft Download Site and try to install them manually. The first step is decompressing. Files are placed on the largest drive (I dunno it based on the total or free space). In my case, one disk drive for a database role is chosen. Then the upgrading procedure starts, with a bug that is:
If the owner of this instance role of cluster is the same computer, the role will be automatically stopped during update process, and will be started later. But while the role is set to stop, the disk drive is offline with it. So, if that drive is the largest, sadly, the update procedure fails — source files of update package are missing.
Even you run these packages manually, not from WSUS, it’s still not possible to choose the folder to decompress. If some drive of database role of cluster is larger than all server self-owned disks, you may want to STOP THE NODE in cluster as a workaround.