As a new decade opens, more and more data centre operators find themselves struggling with an enterprise bottleneck not of their own making.

Servers' hard disk access times have not kept up with the increasing speed of their CPUs, and the resulting lags can be a limiting factor in some database and caching applications, particularly those involving software as a service and cloud computing. As these applications become even more popular, the bottleneck is likely to get worse, analysts predict. And the database appliances designed to target the problem, which have been on the market for years, remain expensive.

Enter flash memory. Until recently, the high cost of flash memory limited it to consumer items with relatively low storage capacities, like digital cameras and MP3 players.

But over the last three years, flash prices have declined an average of 60% a year - a rate that's "faster than has ever happened in the world of semiconductors," according to In-Stat, a market research firm in Scottsdale, Ariz.

This confluence of factors is bringing flash, in the form of solid-state drives (SSD), into data centres.

While it's still early in the adoption curve, analysts predict an increase in the use of SSDs in the enterprise. At its annual data centre conference in December 2009, research firm Gartner called flash-based solid-state storage one of the most important technologies of 2010.

Gartner isn't alone in singing SSDs' praises. "Anybody that's managing and buying storage should be taking a look at the flash options on the market and determining whether it's a good fit for them," says Andrew Reichman, a storage analyst at Forrester Research.

Costing out SSDs

To be sure, despite their declining prices, SSDs remain much more expensive than hard drives on a cost-per-gigabyte basis. Depending on performance, SSDs can range in cost from $3 to $20 per gigabyte, says Jim Handy, an SSD analyst with Objective Analysis, a semiconductor market research consultancy.

Hard drives range in price from 10 cents per gigabyte on the low end to $2 to $3 per gigabyte for enterprise-level, 15,000-rpm models. "The ratio between SSD and HDD pricing is about 20:1 for the bottom end of both technologies, and this will stay in effect for the next several years," Handy says.

Gartner analyst Joe Unsworth puts the average cost of SSDs at about 10 times that of hard disk drives. But cost-per-gigabyte is not the most important factor in some of these access-heavy data center applications. Rather, it's cost per IOPS (input/output operations per second).

The average enterprise-class, 15,000-rpm hard drive achieves 350 to 400 IOPS, says Scott Stetzer, director of enterprise SSD products at STEC, an SSD vendor. The average enterprise-class SSD can push 80,000 IOPS. "It's a world of difference in the level of performance."

Such performance benefits can outweigh the cost differential in certain instances, particularly once you factor in savings from energy costs (SSDs use less energy than hard disks). Applications that require extremely fast location and/or retrieval of data - like credit-card transactions, video on demand or information-heavy web searches - stand to benefit from solid-state technology. Although the total share of the enterprise market that uses enterprise SSDs will remain small, the technology will play an important role in these critical applications, analysts predict.

SSDs in the data centre

SSDs are making their way into data centres in several ways. First, most server vendors are offering SSDs as options, either as a replacement for a hard drive or in addition to one. Salt Lake City-based Fusion-IO even offers an SSD on a PCI card. Second, most storage vendors are incorporating SSDs into their systems. EMC, for example, buys SSDs from STEC and incorporates them into its Symmetrix and Clariion products.

And finally, several companies are building general-use data-access appliances that incorporate SSDs. For instance, Schooner Information Technology, has developed appliances for the Memcached caching system and for MySQL databases. Rather than targeting specific functions like business analytics or web caching, as previous data appliances have, Schooner incorporates flash in an appliance that aims to improve performance of the entire data access tier of the data centre, explains John Busch, Schooner's chairman and chief technology officer.

Where SSDs make sense

SSDs appeared on the radar of data centre operators in the last year to 18 months. "It became an increasingly frequent conversation [with customers] about 13 to 14 months ago," says Steve Merkel, director of solutions engineering at managed service provider Latisys. "We started running a few scenarios where it looked like SSDs would be a reasonable technology to use."

Today, there are two prime uses. The Planet, which runs eight data centres and hosts 18 million websites worldwide, sees customers using SSDs on their host servers to speed web analytics applications, says Rob Walters, director of product management. Latisys sees a similar uptake. One customer, for example, does analytics and profiling of website visitors, then offers up targeted ads. "They have very large data sets," says Merkel. "They can't sit around and wait for traditional storage [response times]."