The new servers are the DS 5100 and DS 6100. They look remarkably like the DX 4000, in fact it appears to be exactly the same case. But inside there is more oomph; both use Intel Xeon processors, the CPU of choice for file servers, and can hold up to 16GB RAM and 16TB of storage. The operating system is Microsoft's Windows Server 2012 R2 Essentials; this is the latest version of Server 2012 but features a simplified interface to make it more friendly to a small business. It is also restricted to 25 users and 50 devices, although this is not an issue in the sort or organisation being targeted by Microsoft and Western Digital.
As with the Sentinel DX 4000, the kit is not exactly cheap. The DS 5100 with 8GB RAM and 4TB storage is £1918, whereas the DS 6100 has 16GB and 16TB storage and costs £3418. This makes them about 1/3rd more expensive than comparably specified Dell kit, although they are a lot cuter.