Storage | Virtual Journeyman

The VSAN story is out and doesn’t seem to be going away any time soon. It feels like everyone I talk to is asking about the product and the pricing model (see VSAN Pricing and Implications). More than once now, I’ve seen a wince or the written equivalent. I can certainly understand, as an extra $15K in licensing to a six CPU cluster is far from trivial. My goal here is to unpack the pricing a bit to examine the value that’s being delivered (the value is non-trivial as well).

Virtual Distributed Switch

Perhaps lost in the discussion of VSAN features is that the VSAN license includes the Virtual Distributed Switch (also known as the vSphere Distributed Switch) for the cluster (since every cluster member is licensed for VSAN). For anyone who’s maintained networking for a group of hosts, this is huge productivity gain, bringing centralized management, consistent naming, “network vMotion” (maintaining network state during a vMotion), Network IO Control (NIOC), and Single-Root IO Virtualization (SR-IOV). These are premium features, normally only available in Enterprise Plus licensing, which bring a lot of value to a VSAN cluster.

Here’s a great note from Punching Clouds on the deployment of 16 VSAN nodes in minutes. This is made possible in large part due to the vDS’s template creation and push deployment capability.

Paradigm Shift – Unbundling Storage Software from Hardware

I think the first time I came across this concept was in a presentation by Jon Toigo http://www.drunkendata.com/ entitled Why Storage Costs So Much and What You Can Do To Bend The Cost Curve. It’s been almost five years, but I actually found the slide I remember.

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But back to the bundling thesis. A major cost is having the storage management software bundled with the hardware appliance. Buy a Tier 1 appliance, pay service and support for upgraded software during the ownership cycle, and at the end, you can’t transfer that software to a new appliance. You buy it all over again. The disruptive model that VSAN brings is the ability to buy the storage smarts independently of the storage hardware and transfer the license to a new piece of hardware at any time in the lifecycle of the hardware. Remember the closed platform of the traditional appliance? VSAN uses commodity x86 CPU cycles to run its software, the same commodity x86 CPU cycles that receive the most development and performance attention due to the sales volume.

I’d also like to point out that VSAN isn’t the first software to take this approach. HP’s StoreVirtual (decended from the Lefthand VSA), Datacore, even the VMware VSA unbundled storage smarts from the array. So there’s even more to the value story, isn’t there?

From RAID to Policy Based Storage

The previous iteration of unbundled storage software and storage appliances relies on RAID hardware controllers to handle resiliency. RAID controllers offload the processing power of RAID-based resiliency from the general purpose CPU to specialized silicon. This was especially helpful with the popular use of parity RAID, before general purpose CPU core counts and processing power went up, and before drive space was expensive relative to processing power. Today, parity RAID is less usefu, per-GB storage costs have crashed, multiple copies of data is the gold standard for data protection. To accomplish this, VSAN uses general purpose CPU cycles to create N+1 copies of the data, determined by per-VM policy.

Ok, what does that mean? In effect, administrators can adjust the policies that affect VSAN striping and number of failures to tolerate on a per-VM basis. Perhaps you determine that one of your VMs needs an increased stripe width to help destage writes or increase the speed of read caches misses. You can make that change for the individual VM rather than for all the VMs on the storage. In addition, you can make that change after deployment.

So what do you think? Does this represent more VSAN Value than you’d originally thought?

After a wide-open public beta, lots of speculation about licensing models and costs, and a long wait, VMware Virtual SAN (VSAN) went GA on March 12, 2014. The basic issue of pricing was revealed: $2,495 per CPU socket for any workload or a $50/user model for Horizon View. What are the implications of VSAN pricing for end users?

Which is the Cheaper VSAN Pricing Model for Horizon View?

With six sockets licensed, anything below 300 users will benefit from per-user Horizon View licensing.

VSAN 6 socket cluster comparison of Horizon View per-user pricing vs. per-socket pricing

I chose a six socket, three host cluster as the smallest likely cluster, but users per socket is the more important stat. What’s revealed is that in any density below 50 users per cpu, per-user pricing is less expensive. As CPU core counts go up and per-socket processing ability increases, the 50 user per CPU socket will probably come into play. Something to keep one’s eye on.

All Cluster Members Must Be Licensed (per socket model)

This might win the award for most obvious reveal in the history of a GA announcement. It honestly hadn’t ever occurred to me that all cluster members would have to have VSAN licenses for their CPUs. In my head, I thought we’d be able to have licensed storage-heavy cluster-members doing the business of VSAN and cluster members without VSAN licenses who wouldn’t provide storage to the cluster but would be able to consume it. That’s not the model. What’s being licensed is the ability to participate in the cluster at all. If after some time, your storage density and growth is fine but you need more CPU, you’ll have to decide whether it would be more cost effective to add a VSAN cluster member without much/any storage or replace a cluster member with a host with more CPU. Or even upgrade the CPUs present in a host, something I wouldn’t have ever thought about doing before this.
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High Entry Level Price

The minimum host count is three and the minimum number of sockets per host is one so I suppose one could make an argument that the entry-level cost of VSAN is $7,485 ($2,495/socket x 3 sockets). In practical terms, purchasing a server with two socket capability and not adding the second socket isn’t done that often. A fully-populated six socket cluster is $14,970 which is getting close to the cost of a storage appliance.

Why don’t we buy single socket hosts for entry level clusters? As an IT administrator, I’d have made the argument for the simplicity of not ever touching the CPU infrastructure. Today, I’m closer to thinking that the advantages of VSAN are enough that we might want to start thinking of purchasing CPU as it’s needed instead of at the time of chassis acquisition. Among the most expensive dollars an SMB can spend are the ones which aren’t needed for over a year. Add the cost of VSAN licensing to the cost of CPU, and that might tip the balance in favor of scaling out CPU as needed. Three CPUs might be enough for entry-level clusters with vMotion and HA.

VSAN vs Storage Appliance (SAN/NAS)

At ~$15K entry level, IT departments might not see VSAN as a clear value play. “That’s almost the cost of XYZ appliance with the drives included!” Well, that’s possible, though it’s a complete apples to oranges comparison. VSAN provides many features you aren’t seeing in entry level storage appliances, but perhaps I’ll save that for another discussion.

What are the implications of the VSAN pricing model on the business of managing storage in IT that you see?

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Category Archives: Storage

VSAN Value and Paradigm Shifts