VMware Server Specs

VMware Virtual SAN (VSAN) is a new hypervisor-converged storage technology that's getting a lot of attention. And for good reason. It has the potential to offer incredible I/O performance at much lower price points (compared to SAN) by leveraging cheap local storage. vsan-pic

But like any new technology, you have to fully understand what VMware VSAN is and how it's going to be applied before you start making cost assumptions and configuration recommendations.

That's why I got into a bit of a Twitter war last week over this article in The Register: "REVEALED: What you'll pay for VSAN software and hardware". I felt they missed the mark on both the technology and the use case. As a result, they over-configured what you really need for VSAN hardware, and came to the wrong conclusion that VSAN will cost as much as a mid-sized storage array.

Dell didn't help things with the tech specs they published and their VSAN configurator. Which should be a lesson to the hardware vendors – you also need to keep your target market in mind.

Where did the article go wrong?

  • Dell PowerEdge R820 – Good server, maybe a little big for this… but ok.
  • Two Xeon 8 core procs – Not bad, no complaint from me
  • 256GB RDIMM – Sounds good to me, but mileage may vary
  • 2 x 400 GB SSD drives – Undersized based on the next item…
  • 14 x 1.2TB SAS drives -16+ TB of raw capacity on one node?

Fully configured, this recommended Dell 820 is about $29K before taxes, shipping, etc. Using this hardware, a 3-node VSAN cluster (the minimum required) would run you $90K in hardware BEFORE paying for the VSAN licensing.

No wonder The Register reaches its conclusion that VSAN isn't all it's cracked up to be. At this price, why wouldn't a small to mid-sized customer just buy three $10-12K dual processor servers and a $50K external hybrid storage array if VSAN – a brand new storage model – is going to cost the same?

The problem is this VSAN configuration is way over-built because they didn't consider the use case. The server is too big and uses a 4-socket machine instead of 2. But the bigger issue is it's trying to stuff a maximum amount of storage capacity into the host without understanding what is actually needed.

The configuration also falls down on SSD Cache size. VMware's VSAN Design and Sizing Guide (see pages 6 & 7) recommends that the SSD drive (flash cache) capacity in the server be approximately 10% of the HDD capacity in the server. The config used by The Register has 16+ TB of raw capacity and 800 GB of SSD, which puts SSD at less than 5% of HDD capacity.

Ignoring the choice of server (an 800 series 4-socket server vs a 600 or 700 series in a dual socket configuration), the main issue is the number of disks and total capacity.

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