Which OS is best for SSDs?

By Lucas Mearian, Computerworld |  Operating Systems, flash memory, Linux

Solid-state disk (SSD) drive architecture can play a big role in how fast a computer boots up and performs. But how big a role the SSDs play -- and how much faster an operating system is -- depends as much on the operating system as on the drive. Although none of the mainstream operating systems now in use have been optimized to work better with SSDs, some do natively work more efficiently than others, according to storage experts.

Of the recent operating systems that have been tested, would you believe the winner so far is ... Windows 2000?

That aging operating system, said Saeed Arash Far, engineering manager at SSD manufacturer Patriot Memory, is markedly faster than Windows XP, Vista, Mac OS X or Linux when using NAND flash memory. Far said his company's tests showed that Windows 2000 is 5 percent to 8 percent faster over its newer rivals because "Windows 2000 doesn't run any applications in the background.

"We're getting ridiculous numbers with Windows 2000," he said. "When it comes to Vista, it is faster than XP, but with XP, you have the luxury of turning off background applications. ... With Vista, you can't."

According to Far, Mac OS X runs "a little faster than Vista" with an SSD drive, but Linux is "always faster" than Vista or Mac OS X -- to the tune of 1 percent to 2 percent -- because like Windows 2000, "it never runs anything in the background."

"If you really want to go inside [the OS numbers], Windows 98 was the fastest of all," Far said. But there's a downside: Windows 98 does not support wear-leveling technology, which evenly distributes data writes to NAND flash memory to ensure no single area of an SSD wears out faster than another. Far said his company's SSDs would wear out in only about a year when running Windows 98.

That brings users who may be wondering about the advantages of SSDs back to the Big Three operating systems: Windows Vista and XP and Mac OS X. The claims and counterclaims about SSD technology and operating systems highlight the intricacies of marrying operating systems designed for hard disk drives with the newer technology of SSDs.

Vista slowing SSD adoption?
In July, SanDisk Corp. CEO Eli Harari said during an earnings call that Microsoft Corp.'s Windows Vista worked so poorly with SSDs and, as a result, was actually slowing the adoption of NAND technology. Harari blamed some "very demanding applications" that, in turn, require more sophisticated SSD controller technology to manage how data is transferred to the drive.

But Harari's claim is one that other disk vendors, including rival Micron Technology Inc., have rebutted.

Using an SSD with a SATA interface, Micron has performed tests on Vista; its predecessor, Windows XP; and Mac OS X, capturing data about the newer drives while booting up the operating systems, installing files, running Office productivity applications and shutting down the computer. Micron found that Vista and Mac OS X performed better with its SSDs than XP, according to a post on Micron's blog site. XP does not align the data in the most efficient way for an SSD -- in 4KB blocks -- while Vista and Mac OS X do, according to Justin Sykes, director of marketing for SSD products at Micron. (Linux, which wasn't tested, also aligns data in 4K blocks.)

"NAND [flash memory] fundamentally has native 4K block sizes. Anything that's not aligned to a 4K block creates extra challenges," Sykes said. "There ends up being background operations to garbage-collect that empty space [in larger file blocks] that isn't fully utilized. And, so that activity is chewing up your bandwidth in the background, and it adds extra wear to the NAND [flash memory]."

According to Dean A. Klein, vice president of memory system development at Micron, Apple's platform seems to perform better with SSDs than Windows systems. "It boots better," he said. "Mac OS does things differently."

When Windows-based PCs boot, the BIOS does "quite a few things" while it's waiting for what would normally be a hard disk drive to spin up, Klein said. "With a MacBook, one thing you'll notice is that it boots up very quick. Our belief is that it's savvy enough to know it has an SSD in it, and it's not waiting for the SSD to spin up, and so takes some shortcuts."

Far agreed that Mac OS X is about 1 percent faster than Vista. But that's not the case when using virtualization applications such as Parallels and VMware's Fusion in Mac OS X 10.5 to run the rival operating system. When running Vista through virtualization at the same time the Mac OS is running, SSD performance is affected.

4KB blocks of data are more efficient
Micron's tests showed that when XP begins writing application-related data, that data is almost never aligned with the beginning of a new NAND page; it begins partway into the page and ends partially through another. "So the controller has to deal with that and come back and clean it up later," Far said. "Vista will start that write on 0 or at 8, for example. So the data structure in Vista is more aligned to 4K blocks."

In NAND flash memory, blocks consists of a number of pages and each page is either 512, 2,048 or 4,096 bytes in size. Therefore, a 4KB block more efficiently fills the memory.

Troy Winslow, marketing manager for the NAND Products Group at Intel Corp., said, "We've even done studies showing 80 percent of all OS requests are in the 4K-to-16K range, yet many SSDs were designed on older controller technology that was requesting large file-size transactions of 128K in size. All SSDs perform best at the smaller file size."

Winslow said benchmark testing on XP and Vista indicated that the less-efficient XP machines show a 10 percent improvement in random input/output operations per second using an SSD instead of a hard drive, while Vista showed a 25 percent improvement under the same conditions.

Pat Wilkison, vice president of marketing and business development at NAND flash memory manufacturer STEC Inc., believes there's no detectable difference in SSDs performance among varying operating systems. "There just has not been any meaningful work done in optimizing for SSD," he said.

Debating defragging
However, one difference between Vista and XP is that Vista, by default, enables background drive defragmentation -- something that isn't necessary with an SSD and can actually wear out the drive more rapidly. While most laptop and PC resellers disable background defragmentation on Vista systems that ship with an SSD, anyone installing or upgrading to Vista may not know they should do that to preserve SSD life, Klein said.

To turn off Vista's auto defragmentation feature, a user would go to the Start menu, then the Control Panel and then choose Control Panel Home. Next select "System and Maintenance" and under the Administrative Tools section, choose "Defragment your hard drive." Vista then allows a user to check or uncheck the Run automatically function.

According to Howard Butler, vice president of technical support at Diskeeper Corp., hard disk drives and SSDs both benefit from defragmentation utilities in operating at peak efficiency. Data may be laid down in contiguous clusters on an SSD, just as with hard disk drives; as it's deleted, space is freed up. But those pockets of free space may be left unused. Defragmentation helps by consolidating data and free space, Butler said.

Joseph Unsworth, an analyst at Gartner Inc., said Vista's SuperFetch feature gives Vista a boost over XP with regard to SSDs because it can preload often-used applications into system memory so they're ready when needed. Vista introduced the concept of low-priority I/O, which enables background processes to run with lower-priority access to the hard drive than other programs.

Unsworth installed Intel's X25 SSD on a PC running Vista and said he was impressed with the boot-up times over the hard disk drive he replaced. While there are now more than 90 SSD vendors, Unsworth said he prefers drives from Intel, Samsung and STEC, which he said offer advanced architectures with multiple channels to NAND flash chips set up in a parallel. For example, Intel has 10 channels on its X25-M SSD. In multichannel NAND architecuters, each parallel channel represents multiple streams of data to multiple NAND chips, yielding greater sustained throughput -- and speed.

When will operating systems be optimized?
Even if operating systems aren't yet optimized for SSDs, they likely will be as the technology gains ground. Last month, at its Windows Hardware Engineering Conference (WinHEC) in Los Angeles, Microsoft promised that its upcoming Windows 7 would work better with SSDs.

Unlike Vista, Windows 7 will turn off disk defragmentation when it detects an SSD instead of a spinning disk drive. Windows 7 will also delete "garbage" data in advance. That would head off garbage collection, which can add latency -- a major factor in the slower write speeds often seen in SSDs.

Microsoft also plans a certification program for SSDs so that the drives properly identify themselves to Windows 7 and prioritize data I/O for the SATA interface.

Regardless of what Microsoft does, Unsworth said he believes that Apple will have the advantage because its OS is closed, meaning Apple can drive its own development initiatives and will likely do so when it comes to SSD optimization.

Apple also plans to launch Mac OS X 10.6, a.k.a. "Snow Leopard," which is expected to trim overhead and optimize it for faster I/O.

"I have to believe they will, and I've told them and recommended to them, wouldn't it be awfully compelling to get boot up with an SSD in under 10 seconds?" Unsworth said. "How easy would that be to convey as a selling point to the consumer?"

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