Hybrid drives boost speed, cut power consumption for laptops, desktops, servers

Computerworld - 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 Corp.'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 Inc. and Seagate Technology LLC 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 Corp., code-named 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% this year. Market prices recently hit $17.50 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% boot-time savings [using ReadyDrive]," he says.

Plummeting Prices The price per gigabyte of flash has fallen by more than the 55% IDC predicted for this year, dropping below the price of DRAM and making the technology attractive as a disk cache for notebooks and PCs. Source: IDC, Framingham, Mass.

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% in some cases and increase usable system life by 8% to 12%, 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.

Jack Weilandt, chief technologist and director of NStar Electric & Gas Corp. in Boston, sees an 8% to 12% increase in battery life as "marginal at best" and adds that faster boot times are mitigated by the fact that "more boot time is spent in authentication and managed desktop component loads than in the loading of Windows itself." But he says the durability of hybrid drives is attractive.

"The key feature to me is that the heads can stay locked for large amounts of time. We put laptops in trucks and carry them to work sites where they can get banged around, so this technology would greatly reduce drive fatalities," he says, adding that a solid-state disk would be even better.

Beyond Laptops

Performance benefits may be the main reason for using hybrid disks in desktops, but Panabaker says some corporate customers have told Microsoft that they'd like to have hybrid drives in desktops so the disk drives will spin down during periods of inactivity, cutting power consumption and heat generation.

The same power savings could benefit servers with direct-attached storage, says Panabaker. And it's likely that ReadyDrive will be integrated into the next version of Windows Server -- though Panabaker won't confirm it. "The code is part of the core bits in Windows," he acknowledges.

The outlook for hybrid disk in networked storage is less clear. ReadyDrive currently doesn't support iSCSI network-attached storage (NAS), but Panabaker says he sees value in supporting it as a way for network storage devices to save power and generate less waste heat in data centers.

Chris Bennett, vice president of core systems at Sunnyvale, Calif.-based Network Appliance Inc., says he thinks the technology might find a niche in small NAS systems, but he sees "no apparent benefit" for enterprise-class systems, noting that NetApp disk arrays already use faster dynamic RAM caches and are not typically powered down.

However, allowing drives to spin down during periods of inactivity could help data centers face heat and power challenges. "In a server environment, power consumption is a big factor," says Rao. "If you can keep disk drives spun down, that saves power."

Falling prices for flash could make it more attractive for network storage, says Panabaker. Flash "is now cheaper than DRAM, so we see an interesting trend where it may be cheaper in really specialized products, such as some high-end SCSI arrays, to use flash," he says.

As performance continues to climb and costs drop, flash is likely to become attractive for more and more applications. Says Rao, "Anyplace there is a gap between processor performance and disk I/O, flash will apply."

Source: Microsoft Corp.

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