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February 12, 2010
• Vol.32 Issue 4
Page(s) 1 in print issue
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Storage In A Flash
Solid-State Drives Are Ushering Data Centers Into A Speedy, Flash-Based Future
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| Key Points
• SSDs boast performance-related benefits that give them the upper hand over conventional hard drives for certain data center tasks, such as online transactional processing.
• Vendors are already prepping products to mesh with SSDs, so future adoption of the storage technology shouldn’t prove to be overly painful.
• Instead of looking to replace all hard drives with SSDs, examine the tasks at hand and consider a hybrid environment to get the best of both storage worlds. | | A flash-based storage continues to enjoy immense success in the mobile sector, the technology is beginning to garner serious attention on far larger scales. SSDs, or solid-state drives, are now a viable storage option for data centers at small to midsized enterprises, thanks to impressive performance and steadily declining prices.
“SSDs are a great investment now and an even greater investment in the future,” says Bryan Martin, enterprise product marketing manager for flash-based storage devices at Dell (www.dell.com). “Immediate benefits and costs savings can be realized with today’s SSD-enabled server and storage solutions. Looking forward, SSDs will continue to break performance records and decrease in costs while architecture developers simultaneously continue to invent and refine solutions.”
 Despite the hype around them, SSDs are by no means a complete and perfect replacement for conventional hard drive technologies, but they do have value for both short-term needs and longer-term strategies. Depending on a data center’s current environment and its business goals, it can pay to jump aboard the SSD train without hesitation.
 Speed Without Compare
According to Rob Ober, a fellow at LSI (www.lsi.com), SSDs have enough attributes that are attractive enough to prompt early adopters—including IT managers, server center architects, and administrators—to spend significant money on deployments. Perhaps the most obvious attribute is performance, as Ober notes that the raw random access performance of SSDs is far higher than even 15,000rpm hard disk drives. He adds that a high-performance array of hard drives can be replaced by 10 or 12 SSDs.
The benefits don’t end there. Ober also points to power savings (thanks to the smaller number of required drives), less vibration (in turn leading to fewer errors), and the fact that hard drives have a large MTBF (mean time between failures), but those failures tend to be random, unpredictable, and catastrophic. SSDs, on the other hand, can wear out as writes accumulate, but those wear-out times are much more predictable.
These attributes can deliver real-world advantages for most data centers, but Martin notes that SSDs are particularly useful for performance-intensive applications with highly random data patterns, such as business processing and decision support systems.
“Business processing applications such as online transactional processing [OLTP] are used by financial institutions and other industries where real-time processing is an absolute business requirement. Stock market transactions are a good example,” Martin says. “In these applications, I/Ops [input/output per second] are a key measurement of performance requirements, and enterprise-class SSDs offer up to a hundred times the I/Ops capability of the fastest hard disk drives. This means a data center using RAID to stripe thousands of hard disk drives within multiple servers to achieve performance requirements can instead utilize a highly reduced number of SSDs to achieve the same performance.”
Jumping In
Moving ahead into the SSD realm generally doesn’t require massive changes to data center infrastructure. In fact, computer system, storage, and I/O controller vendors are already preparing products that accommodate SSDs, says Dr. John Busch, co-founder and CTO of Schooner Information Technology (www.schoonerinfotech.com). Plus, he says that SSDs are compatible with disk drive hardware and programmatic interfaces.
“So deploying SSDs is straightforward,” Busch says. “The data center managers need to decide which applications and data are performance-sensitive and target these for SSD-based systems, and they need to optimize the software with increased parallelism and refined concurrency to fully take advantage of the performance benefits of SSDs.”
Busch says that for most applications, the performance benefits delivered by SSDs compared to disk drives are about 25%, but potential improvements in the future could vastly improve that number. For those improvements to occur, OSes and application-layer software require changes, such as increased read and write parallelism, improved concurrency control, and thread/core affinity management. However, until that happens, SSDs can be used in tandem with another significant trend in data centers: DRAM caching of large data sets.
“SSD technology offers the potential to replace a significant portion of the DRAM in data centers, as well as replacing hard drives,” Busch says. “SSDs are much less expensive than DRAM, dissipate 1/100th the power, and are persistent. As a result, caching of large data sets, which is currently performed in large DRAM memories, can instead be implemented with a combination of DRAM and SSD technology, thereby increasing cache capacity, reducing cost and power, and improving availability.”
Plan To Pair
Instead of viewing SSDs as the wave of the future, data centers could be better served as viewing the storage technology as simply one of two waves. Ober says that SSDs possibly could overtake hard drives in the data center in terms of adoption, but he predicts that each will have its own place in a storage environment.
“Performance requirements can be satisfied by SSDs rather than large numbers of HDDs. Conversely, HDDs are extremely good at storing massive amounts of data at low power and in supporting high-bandwidth sequential data transfers, as well as being indefinitely persistent for archival,” Ober says. “Because of those characteristics, hybrid storage systems will evolve where SSDs will be used for performance and will become more closely integrated into servers—possibly evolving their form factor and interface—and HDDs will take on archival storage and bulk capacity storage.”  by Christian Perry
Action Plan
SSDs won’t serve up a plate of integration headaches for most data centers that adopt the technology, but it remains wise to approach them with a plan in hand. Rob Ober, an LSI fellow (www.lsi.com), offers the following tips to prepare for SSD adoption.
Learn about flash-based storage. It’s like tires on a car—they do wear out and need to be replaced periodically, and higher-performance tires usually need to be replaced more often. But each year, they get dramatically better and cheaper. SSDs also fail in a different way than HDDs but more predictably and in a more manageable way.
Plan for upgrades. Understand what applications and servers are I/O-bound and causing underutilization and where servers doing the same task could be consolidated. This can actually be difficult sometimes, as the CPUs are busy but are thrashing because of waits on storage. These applications are candidates for SSD upgrade and possible server consolidation.
Be SSD-specific. If infrastructure (HBAs, arrays, etc.) is being purchased today that will be upgraded to SSDs, it needs to be developed to handle the performance and characteristics of SSDs. Legacy controllers are a bottleneck today that can limit any benefit of SSDs, while new products are now being developed to fully utilize SSD performance.
Don’t forget software. Begin architecting internally developed software to use the performance of SSDs and design around shorter queues and latency in the storage system. |
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