By Kevin Komiega
EMC has been shipping solid-state disk (SSD) drives in its Symmetrix DMX-4 systems for months. Sun Microsystems is prepping new hybrid arrays that mix SSDs and traditional hard disk drives (HDDs) to accelerate storage I/O. Hewlett-Packard and IBM have partnerships that put SSDs in their respective blade servers to boost storage performance. NetApp is “working on” incorporating the technology into its product line.
With the Tier-1 storage vendors all seemingly on the solid-state band-wagon, it begs the question: Are enterprise users ready for SSDs?
SSDs work with standard drive interfaces and are faster and consume less power than HDDs. Nevertheless, concerns over cost and reliability may delay large-scale adoption of SSDs in enterprise storage environments.
Market research firm TheInfoPro (TIP) has seen a slight jump in the number of Fortune 1000 IT managers looking at the technology, but SSDs are still cost-prohibitive in the minds of most end users.
Research conducted by TIP in 2007 showed just 6% of storage professionals surveyed were using or planning to use SSDs (see figure), while an overwhelming 90% of Fortune 1000 storage professionals said price puts flash-based SSDs out of reach. (Note that the TIP survey was in the spring of 2007; the research firm did not include the question in its more recent surveys.)
At press time, SSD manufacturer STEC, which supplies 73GB and 146GB SSDs to EMC for the Symmetrix DMX-4, quoted a per-gigabyte price for its products of between $12 and $15.
To make a favorable price comparison between enterprise-class SSDs and HDDs, Sun changes the traditional dollar-per-gigabyte pricing scheme into a price/performance argument, using a dollars per I/Os-per-second (IOPS) model.
Michael Cornwall, Sun’s solid-state technology point man and former NAND memory specialist at Apple, says 146GB enterprise HDDs perform at approximately 180 write IOPS and 320 read IOPS for an estimated cost of $2.43 per IOPS.
Conversely, and not surprisingly, 32GB enterprise SSDs blow HDDs out of the water with up to 8,000 IOPS for writes and up to 40,000 IOPS for reads at an estimated cost of $0.08 per IOPS.
Cornwall also points out that enterprise-class Fibre Channel HDDs are declining at about 40% per year, while the price per gigabyte of SSDs is dropping 50% to 70% annually.
But cost is just one concern. The other is reliability, as flash-based storage devices are known to wear out over time.
“Flash cells have a useful life of two-to-three years,” says John Webster, principal IT advisor at the Illuminata research and consulting firm. “You can extend the life of flash units by managing the memory and spreading reads-and-writes across cells evenly over time. You might be able to get more reliability, but it is an issue that must be addressed somehow.”
Webster says vendors need to address the reliability issue before SSDs become a viable alternative to high-performance Fibre Channel or SAS HDDs for mission-critical applications. Flash-based storage is an old concept,” says Webster. “Saying that all of a sudden the IT universe is going to turn on a dime and see incredible value is a bit optimistic.”
Cornwall counters: “The MTBF [mean-time-between-failure] number is reliable. Write endurance issues start to go away once we apply wear-leveling techniques.”
He also says that controller technology bears some of the blame for the problems of the past, calling consumer-level controller technology “anemic” and stating that Sun is working with enterprise controller manufacturers to guarantee reliability and data integrity.
Cornwall says Sun has “seen enough data” to generate MTBF numbers of 2 million hours for SSDs, compared to 1.2 million hours for most HDDs. He adds that flash-based SSDs are also superior to HDDs when it comes to power and cooling requirements, consuming about one-fifth of the power of both memory DIMMs and disk drives.
Illuminata’s Webster does say, however, that SSDs could have a bright future in the enterprise. “If you look back at the evolution of RAID, you’ll remember that RAID levels were created to overcome reliability issues with PC disks. It worked and they became more reliable,” he says. “It’s going to take some time for this to work with SSDs and for users to overcome their concerns.’”