“Caching data in flash is not the right approach,” said hybrid storage vendor Tintri  CEO Kieran Harty at the start of a panel discussion in the Cube at VMworld 2012. “Ninety-nine percent of reads and writes should be on flash with only cold data stored on disk.”

The read-cache only approach, introduced by EMC and more recently NetApp “is the result of bolting flash onto a 20-year-old architecture,” he said. The traditional storage vendors have architectures that are optimized for disk storage. Flash demands a new, purpose-built architecture.

“When these companies add flash they are not rethinking the data layout of the underlying disk system,” explained Suresh Vasudevan, CEO of Nimble Storage. “It is relatively easy to optimize for one medium. Optimizing for two architectures is much more complicated.”

The hybrid vendor architectures are designed to support a combination of flash and storage with most data and all metadata going on the flash and only older, cold data that is seldom accessed on closer disk drives. Nothing in the architecture prevents a customer building an all-flash storage system.

The philosophy at Nimble Storage, Vasudevan said, is that “flash has attracctive characteristics but disk is complementary, and an architecture that provides both the high performance of flash and the high capacity of disk at a lower cost without the need for manual reconfiguration provides the best solution for most business applications.”

‘Virtualization has changed what we need from storage dramatically,” added Rohit Kshetrapal, CEO of Tegile. Virtualized environments need high IOPs and a better method for achieving that performance than striping the data over a large number of disks. “Flash does caching very well and is very fast but dos not store large amounts of data for long periods extremely well. So combining them gives you a Prius at the Tesla level combined with the ability to store the data cheaply.”

Nimble and in particular Tintri and other hybrid vendors also offer much greater integration with vCenter, allowing the storage to be managed from the virtualization layer rather than separately at the hardware layer.

Midsized companies have made up the bulk of the early adopters of hybrid storage systems have been midsided companies in part, says Harty, because they have shorter replacement cycles. However, all three have large enterprise customers including several large media companies and banks, and they all foresee a steady growth in the enterprise end of the market.

Wikibon and SiliconAngle will be webcasting live from WMworld 2012 through Wednesday, August 29, with interviews with the thought leaders of the virtualization revolution. Catch the action at SiliconAngle.tv.