Why SSDs Won't Knock Out Disk Drives Anytime Soon

SANTA CLARA, Calif.—Solid-state drives replacing spinning disks in laptops and servers is trendy as a news topic for publications such as eWEEK, but they're hardly making much of an real impact on the world at the moment. After all, only 473,000 of them were sold worldwide in 2007, and the total number sold in 2008 probably won't reach 1 million, according to industry analysts.

In contrast, spinning disk drives continue to sell well into the tens of millions each year.

But don't worry. SSDs will have their day in the sun, and it could be sooner rather than later. The advantages far outweigh the disadvantages of the form, analysts speaking at a panel session at IDEMA DiskCon 2008 said Sept. 16.

NAND flash memory, which has much faster read/write performance than conventional disk drives, forms the core of the removable USB storage devices known as USB flash drives, as well as most memory card formats now available. Apple's iPod and iPhone are two of the most successful commercial usages of NAND flash.

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Most industry experts at DiskCon agreed that SSDs will start taking off in overall usage in the 2011-2012 time frame.

"The main issue with NAND flash is that it never gets any better in performance—it only gets worse over time," Joe Unsworth, NAND flash analyst with Gartner, told attendees here at the Hyatt. "Data retention certainly remains a major issue, too. The endurance cycles are still too low, and when the process geometry gets to be two times and three times in production situations, watch out."

These limitations put much more pressure on storage controllers—which are the storage system traffic cops—to fill in the gaps left by SSDs, Unsworth said. To the industry's credit, controller makers such as Adaptec, AMCC and Emulex are coming up with improved components to do the job.

Still, there is a lot of corporate interest in moving SSDs into key positions in data centers, Unsworth said, and for good reason.

Big Advantages for Data Center Swap-out

"I know of a deployment in which a company swapped out four HDDs [hard disk drives] for two SSDs, running on a Sun Solaris implementation," Unsworth said. "One SSD was for read, the other for write. They ended up with 10 times improvement in read/write speed, which to them was important, and five times less power drawn out of the wall, just for making that one change. Those kinds of numbers become huge when applied to large implementations."

Due to a glut of NAND flash now sitting in warehouses waiting for customers, prices are starting to come down, but it is still much more expensive than spinning disk storage. Wholesale NAND is currently priced at about $2 per gigabyte, spinning disks at about 30 cents per gigabyte.

"Frankly, SSDs for use in laptops are not really a compelling buy at this time," said Jim Handy, a longtime NAND flash analyst with Objective Analysis. "There is a $500 to $600 premium you have to pay if you want to swap out a regular HDD for a solid-state drive right now [in Dell, Samsung and Lenovo laptops]. You really don't get that much in return for paying that premium.

"They're a little faster in performance, and they use less power—but not that much power—and most users believe regular HDDs are fast enough to do what they need to do."

Handy said that the SSD in the enterprise data center—working inside servers and storage controllers—is a much more interesting proposition at this time.

"NAND flash is finally cheaper than DRAM, and it could be that NAND will start replacing DRAM in a lot of the newer servers," Handy said. "It makes sense in the economy of scale. SSDs save space [and] power, cooling and maintenance costs over HDDs and are less expensive now than DRAM."