Solid state drives are encroaching on hard disk drives with the promise of faster access to data, but hard disk drives are fighting back—in some cases, with built-in solid-state storage of their own.

On Tuesday, Seagate Technology took the fight to the enterprise market, introducing its Seagate Enterprise Turbo SSHD, which it calls the world’s first enterprise hybrid drive. Shipping now to server and storage vendors and resellers, the new drive is also available as an option in IBM System x servers.

Many enterprises are adopting SSDs for the data they need to access most often and most quickly. Though far more expensive per gigabyte than HDDs, solid-state flash devices can read and write data much faster. SSDs in many cases are taking the place of the fastest HDDs, which spin at 15,000 rpm but still don’t match the speed of flash storage, said Forrester Research analyst Henry Baltazar.

The Enterprise Turbo combines a 2.5-inch, 600GB 15K drive with 32GB of flash cache. It will cost just slightly more than a conventional 2.5-inch 15K drive and offer more than twice the speed, according to Seagate. It's as much as three times the speed of a conventional 3.5-inch 15K drive.

Hybrid drives are already available for consumer systems, including Apple’s iMac. The Enterprise Turbo is built for enterprise use with higher reliability, tolerance for rotational vibration and other features, the company said.

“With the rise of flash storage, the number-one thing that’s at risk is the 15K drive,” Baltazar said. Seagate, a major vendor of such drives, has a lot at stake in that transition even though the company has already entered the flash business itself, he said.

With the hybrid drive, Seagate seems to be staking out a middle ground, overcoming some of the limitations of the traditional 15K drive. Deployed inside an individual server, such a drive would have its advantages, including faster startup times and fast access to often-used application data, Baltazar said. However, many large enterprises are looking at using flash separately from HDDs, such as installing flash cache in servers for speed but keeping low-cost drives on a SAN, he said.

“This could be a bit of a stopgap ... but the popularity of flash is already growing,” Baltazar said.

Updated 10/4/2013 to reflect the size of the Enterprise Turbo drive at 2.5 inches.