VMware Virtual SAN Move, Explained

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VMware moves into a new market with the introduction Wednesday of Virtual SAN, which will provide a newly defined tier of storage in the datacenter. Virtual SAN combines two types of physical storage -- hard drives and solid-state disks -- into a virtualized pool that can be managed through the hypervisor.

Managing virtualized resources is the new pivot point in the datacenter, and no one understands that better than VMware. Virtual SAN is VMware's direct leap into software-defined storage, first announced in a beta version at VMworld last August. It also continues working on its NSX software-defined networking platform. When combined with its existing server virtualization product line, Virtual SAN takes the company a big step closer to its ultimate goal: the software-defined datacenter, a combined set of virtualized resources that will be managed jointly from a single console.

Virtual SAN is not a new storage device or storage technology but a way of managing the storage in a rack full of virtualized servers, without needing any other specialized storage software. Virtual SAN is embedded in the vSphere kernel; vSphere is VMware's management environment for overseeing dozens or thousands of virtual machines. As virtual machines are provisioned, they will be assigned storage through two clicks on the vCenter management console.

Virtualization users "are struggling to keep up with the demand for storage," said Alberto Farronato, VMware's director of product marketing. Adding lots of storage from various manufacturers and with different storage management software "didn't simplify things," he added.

[Want to learn more about how VMware is trying to enable the software-defined datacenter? See VMware Navigate High Wire Act.]

With Virtual SAN, server-based storage is near the CPU and has the shortest access route over which to deliver its data, compared to external devices and arrays. Virtual SAN uses the SSDs on the server as a write buffer and read cache, according to early reports on the product. In that way it can speed up I/Os over its short route to the CPU.

A Virtual SAN node can host up to 32 disks and 100 virtual machines, giving the maximum 32-node Virtual SAN the capacity to host 3,200 VMs and 4.4 Pbytes of storage space. The same maximum Virtual SAN can manage 2 million read-only input/output operations per second or 640,000 read/write IOPS, Farronato said. The system scales linearly, so a 16-node Virtual SAN would support one million IOPS.

Despite capacities that could fit many enterprise storage needs, VMware spelled out a limited likely set of use cases for Virtual SAN, perhaps with an eye toward not playing an overly disruptive role in the storage market. That would smooth the transition for its existing virtualization customers, and lessen the upset for partners of heretofore VMware-compatible storage systems.

Farronato emphasized that Virtual SAN "is a new tier of storage in the datacenter," not a replacement for existing tiers. But his description of the ease of implementation and smooth operation with other vSphere functions might mean customers will find additional uses beyond the ones identified by VMware. For example, VMware sees Virtual SAN as applicable for tasks "such as Virtual Desktop Infrastructure (VDI), test/development, and disaster recovery," he said. But if it's good for such uses, there are many others that could be served by a high performance, on the server storage system.

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Virtual SAN will come in two forms initially, Farronato said. One is servers coming from 13 manufacturers that have been certified as Virtual SAN Ready Nodes. Suppliers will include IBM, Cisco, Fujitsu, and Dell. Or customers may choose from 150 certified components to build nodes of their choice. A Virtual SAN server will have hard drives, like other servers, but it will also have at least one or more SSDs and a RAID controller.

Getting Virtual SAN into the datacenter will strengthen VMware at the new pivot position. Most of the storage traffic generated by a virtual machine must move through the hypervisor, giving VMware a vantage point under its supervision that can provide guidance on what future storage systems might be needed as the datacenter evolves. It also gives it a position from which to watch application performance and perform remedies if slowdowns occur.

Farronato said Virtual SAN works with other key vSphere management functions, including such data services as backup, cloning, replication, and snapshots. It also works with vSphere's Distributed Resource Scheduler, High Availability, and VMotion. The last is particularly important, since if the popular VMotion live migration function is used, then so will the VMware file storage system, which eliminates some potential storage competitors. Farronato, however, emphasized the wide number of storage devices that Virtual SAN can work with.

Virtual SAN, unlike storage systems that are more external to the hypervisor, uses about 10% of a CPU to perform storage functions for virtual machines, he said. And once the storage on a set of servers is pooled under Virtual SAN, the storage is immediately available and follows the virtual machine around as it's migrated. The user avoids the need to set up external disk arrays and LUNs to get a storage system up and running in support of virtualized hosts.

The software-defined storage approach allows policies governing what storage applications should receive to be contained in a set of policies that get applied by Virtual SAN as it provisions a virtual machine.

Virtual SAN has been in beta for six months, and VMware says it's been tried by 12,000 customers. It is priced at $2,495 per server CPU. A version for virtualized desktops, Virtual SAN for Desktop, is priced at $50 per seat.

Solid state alone can't solve your volume and performance problem. Think scale-out, virtualization, and cloud. Find out more about the 2014 State of Enterprise Storage Survey results in the new issue of InformationWeek Tech Digest.