Computerworld

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.

Page Break

Jack Weilandt, chief technologist and director of NStar Electric & Gas Corporation, sees an 8 percent to 12 percent 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.

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 Network Appliance, 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."

Falling prices for nonvolatile flash memory have prompted some notebook manufacturers to go beyond hybrid disks and announce systems that replace the entire hard disk with a solid-state disk (SSD). In June, Samsung Electronics Co. introduced two notebooks for the Korean market -- the Samsung Q1 and Q30 -- that use a 32GB flash-based SSD that looks like a standard 1.5-in. ATA hard disk drive. In July, Sony launched the Vaio UX90 micronotebook, which includes a 16GB SSD, for sale in Japan and China.

Compared with units with hard drives, SSD-outfitted notebooks boot up and run faster, are quieter and use less power. Samsung claims that its units will boot up 50 percent faster. But they aren't cheap. Sony's UX90, which sells for $US1805, costs $343 more than a unit with a 30GB hard disk. The Samsung notebooks start at $2430. At current prices, 32GB of flash might add $700 or more to the price of a notebook, says IDC analyst John Rydning.

The price of flash, at about $17.50 per gigabyte, has already dropped below IDC's predictions. However, that pales in comparison to disk drives, which cost as little as 65 cents per gigabyte. Disk drives also enjoy economies of scale -- their cost per gigabyte decreases as capacity increases. In contrast, flash pricing tends to be linear. The crossover point for SSD versus traditional hard drives is 10GB, says IDC analyst Dave Reinsel. At capacities above that, hard drives are cheaper.

Today, flash SSDs make the most sense in rugged notebooks for military or industrial use. That's the case at NStar. "The hybrid disk-drive technology is somewhat attractive to us, but I believe that the flash-only drives will be a much better model for us in the future when the pricing of high-capacity flash gets more into the range of commodity pricing," says Jack Weilandt, the energy firm's chief technologist.

Costs will have to come down further and SSD capacity will need to expand before flash SSDs are viable in broader applications, says Rydning. He notes that while the disk footprint for Windows XP is 1.5GB, Vista is expected to come in at between 5GB and 15GB. "That eats up a pretty big chunk of the solid-state disk," he says. Weilandt is less worried. "For many applications, 32GB is more than sufficient for business use," he says.

Given the predicted declines in flash pricing, Don Barnetson, director of flash marketing at Samsung Semiconductor, thinks general-purpose notebooks with SSDs might not be too far off. "I think you'll see [some systems] this year," he says. "But it will go into the mainstream in three to five years."