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Hybrid drives promise better Vista performance

Flash memory to boost speeds

Your next Windows laptop could run faster and last longer on a single battery charge thanks to a series of hybrid hard disk drives and a feature in the Windows Vista OS (operating system) that leverages Nand flash memory as a disk cache.

The feature, called ReadyDrive, could also reduce the incidence of hard disk crashes resulting from shocks – the most common hardware failure in notebooks – by decreasing the amount of time the disk needs to be spinning.

Notebooks will be the first systems to leverage the technology, but its potential is much broader, said 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 said.

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

Big 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," Panabaker said. This year market research company IDC predicted that flash prices would drop by 55 percent. Halfway through 2006 prices have already exceeded projections. Current prices have dropped into the $17.50 (about £9.50) per GB range, and the trend is expected to continue.

Because disk I/O (input/output) speeds haven't kept up with CPU horsepower gains, it was just a matter of time before storage vendors turned to flash. Vista was certainly the catalyst, said IDC analyst John Rydning, but the use of hybrid drives could well 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 flash device could be removed at any time, however, unique data cannot 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 OS to facilitate faster bootup and resume times. "I would expect to see 30 percent boot time savings [using ReadyDrive]," Panabaker said. During normal operations, data retrieved from the cache will be transferred two to three times as quickly as from disk, Panabaker said. 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 be the bottleneck. Therefore, some applications that read sequential strings of data – such as video – won't see as much benefit.

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 to 12 percent, said Don Barnetson, director of flash marketing at 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," he said.

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 platform will include 256MB of flash and can look like a ReadyBoost device or a hybrid disk accessible to ReadyDrive, said Kishore Rao, product line manager.

A standard hard disk includes both magnetic storage platters and a small DRAM buffer. A hybrid drive adds flash memory, which is used as a non-volatile data cache. Data in the cache can be retrieved faster and reduces use of the hard disk, cutting power consumption.

Panabaker said hybrid drives are a better design for ReadyDrive, since they keep the cache and disk under the management of the storage subsystem. "Microsoft has concerns about the issues associated with such a separated nonvolatile cache," he said.

"We don’t see that as being an issue," said 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, while Intel counters that the hard disk is more likely to fail, and when that happens the user must throw out the flash along with the disk.

"It's difficult to predict how this is going to play out with PC manufacturers," said Rydning at IDC. But users aren't likely to care, as long as computers that use the technologies perform and cost the same.


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