VSan a work-in-progress in VMware software-defined storage plan

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VSan a work-in-progress in VMware software-defined storage plan

Antony Adshead

VMware has reiterated its software-defined datacentre vision of the future at the VMworld Europe 2013 event in Barcelona, attended by 8,500 people this week. A key component of the jigsaw is software-defined storage. But does the VMware vision for storage hang together?

The general IT backdrop painted by VMware, and the justification for the software-defined vision as a whole is one of transition from siloed IT, that is “brittle”, “hard” and difficult to manage, to IT-as-a-service via millions of next-generation apps delivered to billions of users and increasingly via mobile devices and the cloud.

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The VMware answer to this trend is to virtualise everything in the datacentre – servers, networks and storage – with control abstracted to a software layer above the hardware.

In his keynote speech VMware CEO Pat Gelsinger (pictured) set out the VMware vision for the storage element of this software-defined future. “Storage is a complex, hard problem that we want to see aligned with application demands,” said Gelsinger.

Traditional storage, he said, is based on hardware resilience, the world of the storage array. The future, he said, will comprise scale-out infrastructure, increasingly with direct-attached storage.

Fleshing out the VMware software-defined storage vision, Gelsinger set out the three key requirements. These were that is should dynamically match storage to application demands, provide automated delivery of storage to service level agreements, and provide pooled storage resources.

Going further, the CEO described storage that would be policy driven, with apps matched to capacity and performance, and application-centric with services, such as replication, snapshots, data deduplication and cloning, built into software and applicable on a per virtual-machine basis.

The VMware products that address these needs are led by VSan, which was previewed at last year’s VMworld Europe and announced formally at VMworld in San Francisco this summer.

VSan is Vmware’s storage virtualisation software. It creates single pools of storage for vSphere workloads from distributed direct-attached storage, third-party vendor arrays, white box JBODs etc. Likely maximum capacities for a VSan pool indicate it will be in the petabyte class, meaning it can in theory pose a threat to SME and midrange-to-entry-level enterprise storage arrays.

VSan is available now as a beta and will be available generally in the first half of 2014.

Aspiration is there to provide storage functionality in vSphere of petabyte capacities and with advanced storage services

The trouble with all that is that it doesn’t amount to an enterprise class of storage provision. And Gelsinger admitted as much, slating VSan for use with “VDI, tier 3 storage and branch office” use cases.

So, is there something missing in the VMware vision?

Questioned further, Gelsinger admitted the company’s idea of a software-defined storage future, at least at enterprise-class, is mostly just that for now – a concept.

“We’ve laid out a broad vision today; it’s not complete,” he said. “We’ve talked about the control plane and talked about being able to match apps to storage requirements with, for example, platinum, gold and bronze service levels. And we aim to do this with VSan and VVols capability. But VSan is currently at version one. It doesn’t have the feature richness it will have in versions two and three nor the nine's reliability it will have in future versions.”

The question is begged: why does VMware’s vision of software-defined storage seem to stop at around about the midrange?

It’s mostly a matter of time, said VMware senior director of product management Gaetan Castellan.

He set out a model of storage needs split between “hot edge” and “cold core” storage requirements. The hot edge comprise high performance workloads, typically targeted by flash storage currently, and requiring fast I/O. The cold core comprises the bulk storage typified by high capacity spinning disk and lower levels of throughput.

VSan targets the hot edge, said Castellan. But if that’s the case, why did Gelsinger lump VDI (presumably a high performance workload) alongside tier 3 and branch office uses?

“Because VDI is high performance but not so mission critical. For now VSan doesn’t have the data services, the service levels to deliver, say, synchronous replication for example,” said Castellan.

In other words the aspiration is there for VSan to provide storage functionality in vSphere of petabyte capacities and with advanced storage services, such as replication, snapshots, data deduplication and more. Unfortunately, VMware executives present at the event wouldn’t be drawn on when that would be.


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