Flash forward to no disk crashes

Your next Windows laptop could run faster and last longer on a single battery charge, thanks to a new generation of hybrid hard disk drives and a feature in Windows Vista that leverages NAND flash memory as a disk cache. The feature, called ReadyDrive, could also reduce the incidence of hard disk crashes due to shocks -- the most common hardware failure in notebooks -- by decreasing the amount of time the disk needs to be spinning.

The technology will first appear in notebooks, but its potential is much broader, says Ruston Panabaker, an architect in Microsoft's Windows hardware innovation group. "We fully expect to see it show up in desktops and perhaps even in specific server applications," he says.

ReadyDrive has spawned a new category of flash-assisted hard drives. Samsung Semiconductor and Seagate Technology have each announced hybrid drives that integrate a 1.5-in. magnetic hard disk with up to 256MB of onboard flash. Both are expected to be available early next year. A rival technology from Intel, codenamed Robson, places the cache on the motherboard along with a controller chip. It will launch with Intel's Santa Rosa notebook platforms in the first quarter of 2007.

Improvements in the performance of flash chips and plummeting prices have made the new hardware designs viable. "The interface to flash chips has been doubling in read and write performance every single year," says Panabaker. Research firm IDC predicted that flash prices would drop by 55 percent this year. Market prices recently hit $US17.50 per gigabyte, which is already less than projected, and the downward trend is expected to continue.

Because disk I/O speeds haven't kept up with CPU horsepower, it was just a matter of time before storage vendors turned to flash. "Vista was certainly the catalyst," says IDC analyst John Rydning, but the use of hybrid drives could certainly expand beyond Windows systems.

A related Vista feature, ReadyBoost, is a read cache that allows Windows to cache memory pages that won't fit into main memory on a USB flash drive. Because the device could be removed at any time, however, unique data can't be stored on it, and data is encrypted for security reasons. "The final solution is ReadyDrive," a write cache that can cache portions of the operating system to facilitate faster boot-up and resume times, says Panabaker. "I would expect to see a 30 percent boot-time savings [using ReadyDrive]," he says. During normal operations, data retrieved from the cache will be transferred two to three times as fast as from disk, says Panabaker. Samsung claims that the cache in its hybrid drive is 50 times faster than disk.

Not all applications will benefit equally from hybrid disks, however. The biggest performance improvement comes from faster seek times -- the time it takes to locate data on disk. Those latencies, more than transfer rates, tend to produce a bottleneck. Therefore, some applications that read sequential strings of data, such as video, won't benefit as much.

Windows, however, is more transactional. It tends to trickle log files and other data even when systems are idle, keeping drives spinning. Placing that data in the write cache allows disk drives to power down. That could reduce power consumption by up to 90 percent in some cases and increase usable system life by 8 percent to 12 percent, claims Don Barnetson, director of flash marketing at San Jose-based Samsung Semiconductor. Hybrid disk drives will also be more reliable. "The hard disk drive is able to withstand shocks when it's in an off state. We can improve the reliability up to five times," Barnetson says.

While hard drive makers advocate a hybrid disk drive that places flash memory cache with the physical disk drive, Intel thinks the cache should be on the motherboard. Its Santa Rosa notebook will include 256MB of flash and can look like a ReadyBoost device or a hybrid disk accessible to ReadyDrive, says Kishore Rao, NAND product line manager at Intel. Panabaker thinks hybrid drives are a better design for ReadyDrive, since the storage subsystem manages the cache and disk. "Microsoft has concerns about the issues associated with such a separated, nonvolatile cache," he says.

"We don't see that as being an issue," says Kishore, adding that Intel's Matrix storage manager chip will safely handle all I/O operations. Disk drive makers say problems with flash on the motherboard will be harder to service. However, Intel counters that when a hard disk fails, it would force the user to throw out the flash along with the disk. "It's difficult to predict how this is going to play out with PC manufacturers," says Rydning. But users aren't likely to care, as long as the technologies perform and cost the same, he adds.

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