VMware announced on March 12, 2014 that its VMware Virtual SAN (VSAN) product was moving out of beta and would be generally available to customers. A much anticipated product, VSAN offers a huge list of features and addresses a number of customer use cases. So what is remarkable about this product, other than that it serves up a bunch of disk storage to systems providing high performance and other benefits?

To better understand, let us take a brief detour into how we have arrived at this point. In the past, disks were directly connected to systems as Direct Attached Storage (DAS), as shown in the diagram below.




This addressed most customer needs but also had several critical limitations. Storage availability was tied to host system availability, and available storage capacity on one host could not be used elsewhere. Data protection needed to be setup and configured manually, or with specialized disk adapters.

In order to resolve these issues, storage moved to the network and storage capacity could now be shared between multiple systems. Specialized storage controllers supported high performance, offered large capacities, supported multiple host platforms, and were highly available. However, more effort was involved with the configuration and setup of these network storage systems.

There are two major types of network storage – Storage Area Network (SAN), and Network Attached Storage (NAS). This classification is based upon whether they serve block storage (SAN) or file storage (NAS). The diagram below shows the various components of a SAN storage system.




A summary of the benefits and limitations of DAS, and the solution provided by the network storage approach is listed below.

Over the past few years, the performance of network storage systems has greatly increased. A number of features have been integrated into the storage controllers making them more intelligent. However, newer systems impose larger demands on performance of network storage systems. The storage based on spinning disks is unable to keep up with requests from host systems. Network storage has become quite expensive as well, since it provides a large feature set with most features being rarely used.

During this time, standard systems and disks kept increasing performance and reducing in price. This has created the need for a simple, inexpensive, and policy-driven storage platform, which is what VSAN represents.

The table below summarizes the benefits and limitations of network storage, and the solution offered by the VSAN platform.

VSAN is a distributed DAS solution implemented on multiple systems, but without the major limitations of DAS and network storage. It is simple and inexpensive, but also available and reliable. There are no islands of storage, and performance and capacity scale together. VSAN software enables all the distributed storage to function as a single logical pool. Storage policies can be seamlessly implemented, and solid state disks effectively mask the latency of spinning disks.

The significance of this technology lies in its parallels to other popular technologies. What are these technologies, and why were they revolutionary? Watch this space for Part 2 of the VSAN technology story.

Ravi_PicRavi Venkatasubbaiah is an IT executive and business leader with 20+ years experience helping companies manage adoption of emerging technologies. Ravi serves on the Board of Directors at VMware User Group, and as a leader of the Silicon Valley VMUG chapter. He enjoys working with entrepreneurs in Silicon Valley and India, and is an advisor on Strategy, Technology, and Operations. He currently lives in San Jose and blogs at meluku.com.


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