Updated: The Pros and Cons of SSD in the Enterprise

By Pam Baker

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Editor's Note: Because solid state drive technology is continuing to progress in the areas of TCO, durability, speed, and energy consumption we thought it would be a good idea to update our first pass at the pros and cons of this technology to see what has changed and where the advancements are taking the adoption curve.

Buzz surrounding solid state disks (SSD) is at an all time high and growing daily. For consumers that can pony up the price, the choice between hard disk drives (HDD) and SSDs is a slam-dunk. For enterprises, the question is a bit stickier and not just because of the per-unit sticker price.

"The relatively high expense of SSDs is only worthwhile if you actually reduce overall complexity and cost for your virtual machine (VM) environment," said Ed Lee, architect for storage start-up Tintri and a member of the original Berkeley RAID team. "Eliminating complexity and packaging this technology in a form that solves VM storage problems requires re-examining how storage systems are built from the ground up."

Given that VMs are the order of the day in enterprise IT, this particular sticking point is problematic. SSDs suffer from "write amplification" and latency spikes. "Custom-designed flash has the potential to avoid some aspects of these problems, but requires using non-standard, non-commodity products, which are very expensive and require lots of custom software," said Lee. "Fortunately, intelligent software techniques can circumvent the write amplification and latency spike issues of commodity SSDs."

The biggest barriers to SSD adoption for VM applications, then, are cost per gigabyte of SSD and delivering flash technology in a form that works well for VMs.

To SSD or not

The storage industry has been trapped within the confines of HDD so long that it's hard for them to visualize another way. There's the draw of familiarity and the fear of the new to overcome.

"SSDs are a profoundly different media than mechanical disk and promise to be a game-changing tool in continuing to improve application performance," explained Matt Kixmoeller, VP of Products at PURE Storage. "They combat the dramatic data growth and increasingly randomized I/O issues that are currently stressing the data center."

However, he said, advancements in the internal architecture of enterprise storage arrays to better handle flash "will be a crucial step in adopting this technology," because current-generation arrays that were built for rotating disks simply can't meet the demands of flash.

"SSD technologies are game changing and they drive a whole new thought pattern around persistent storage," agreed Burton Group Analyst Gene Ruth.

This has led to a prevailing preference for hybrid data centers combining both HDDs and SSDs in a multi-tiered approach. The SSDs are in the top (logical) tier, providing access to selected high-volume and high-demand data, while the HDDs are in a lower tier, supporting bulk storage and lower-demand data. Intelligent algorithms decide the data split between tiers, although there are some concerns that critical processes can accidentally end up in the wrong tier.

"The current 'best practice' in large data centers is to use (relatively) small-capacity drives and only partially load the drives," said Michael Willett, storage security strategist with Samsung. "This results in more aggregate read/write heads and better performance moving data dynamically. At these smaller capacities, SSDs are currently more price-competitive."

Thus total cost impact is likely to take precedence over unit costs. "The decision to purchase SSD is almost always driven by a compelling return on investment (ROI)," said Ron Lloyd, product marketing manager at EMC Corp. "The combination of SSD technology, SATA technology, and advanced quality of service software features has changed how customers evaluate and plan their storage investments."

The pros ...

Recent Improvements - Over the last 18 months, SSDs have grown to support a much larger feature set including compression, de-duplication and AES-256 encryption. "Performance has also improved with new controllers leveraging the SATA III 6Gbps interface and current generation SATA III SSDs can now achieve more than 500MB/s read/write, which is nearly double what previous generation SSDs were doing not long ago," said Alex Mei, CMO of OCZ Technology. "In addition, PCIe based SSDs are now delivering 4K random write performance of well above 100,000 IOPS making them even more viable for tiered storage solutions."

Energy efficient - "Using SSD technology reduces the overall power consumption of devices such as disk arrays, servers and laptops, but also improves their performance and environmental ruggedness," said Jieming Zhu, distinguished technologist at HP StorageWorks.

Speed - In short, SSDs are blazingly fast. They are even great for developers doing complex and/or big builds. "The spreadsheet math on solid state disks is simple: They allow you to do more, faster builds so that QA teams don't to wait as long and customers get the products sooner," said David Intersimone, VP of Developer Relations and chief evangelist, Embarcadero Technologies.

Several of his company's developers use SSDs for local builds as well as larger product builds.

"The savings and time to market, as well as the speed and stability make it simple to choose SSDs."

Performance - "Solid state drives continue to offer a performance premium over other storage solutions and that gap continues to widen," said Mei. They are more reliable, but they are also more rugged, energy efficient and a "greener" option.

Durability - "SSD is designed to operate in more extreme environments of up to 70 degrees Celsius. With no moving parts, SSD drives are less fragile and silent than hard disks, which are more susceptible to operational and non-operational shock and vibration," explained Zhu.

Control of unstructured files - The incredible rise of unstructured data is having a dramatic impact on storage and data management applications.

"We're seeing growing demand for specialized storage systems, including storage media that give users the control or flexibility they need to manage unstructured files over their lifetime," said Jon Affeld, senior director of Product Marketing and Business Development at BlueArc , a provider of high performance, unified network storage systems. "In the near term, it will serve as a powerful caching tier for fast access to files that are in high demand. Moving forward, we can expect the use of SSDs to get more sophisticated as we see data management applications incorporating more powerful search, classification, archiving and retrieval functions."

Compatibility with operating systems - "All SSD vendors provide existing input/output storage protocol compatibility, interoperable with the existing operating system storage stack," said Zhu.

Caching - Storage virtualization software helps shape the shared storage infrastructure required by virtual IT environments and takes good advantage of SSDs where appropriate, reducing the write duty-cycle by caching upstream of the cards to minimize actual writes to media. This effectively extends the useful life of these premium-priced assets.

"It can also make modest sized SSDs appear to have much larger logical capacity by thin provisioning its resources," said Augie Gonzalez, director of Product Marketing at DataCore Software. "The sage advice is consider SSDs as one element of the physical storage configuration, but put your money on device-independent storage virtualization software to take full advantage of them."

The cons …

Cost - SSDs remain more expensive than HDDs. One of the major reasons behind many growth predictions is the expectation that consumer grade NAND memory prices will continue to decline and enable much lower unit costs.

"The fallacy of this assumption is that most of the cost estimates are based upon the expected reductions of consumer-grade multi-level cell (MLC) NAND memory chips," explained Joel Hagberg, VP of Enterprise Marketing in Toshiba Storage Device Division. "In order to provide the reliability required for enterprise applications, most SSD vendors are using more expensive single-level cell (SLC) NAND memory chips or enterprise grade MLC (eMLC) NAND chips, which will not follow the aggressive consumer grade NAND price reductions."

Questionable life expectancy - NAND Flash, the underlying technology of today's majority SSD products, has write wear-out limitations, with embedded processors, software and over provisioning of capacity, among other things," said Zhu. SSD manufactures have addressed this limitation, however, this inevitably adds another link in the chain of the overall reliability of SSD-based systems that must be rigorously tested and certified. "The lack of standard measurement of the life expectancy of SSD is a major drawback," Zhu warned.

Capacity - There has been a rapid increase in capacity, said Mei, reaching levels as high as 2TB for a single SSD. Even so, HDDs still have a significant advantage in both overall storage capacity and price per GB.

Technology is nascent - HP and other industry leaders including Intel and Sun/Oracle do not predict that SSD will replace hard drives in the enterprise. "Like any new technology, SSD is still at the testing stages so there are a number of factors and challenges that need to be addressed before it matures in the enterprise space," said Zhu.

Not ideal for all - "SSD is not recommended for everyone. It is ideally suited for businesses that require high-performance, intensive I/O operations; are power sensitive; and/or are in a rugged environment," said Zhu. HP expects SSD to be used as a premium performance tier in well balanced storage deployments.

SSD vendors are improving the technology everyday and the list of pros and cons will fluctuate accordingly over time. "HDDs have had 53 years of research and development to refine the electro-mechanics -- the rotating media, moving read/write arms, etc. -- of the components and to squeeze every possible refinement into that technology, based on magnetism, explained Willett.

"By comparison, SSDs have had only a relatively few number of years to refine the underlying technology of solid, unmoving electrical components, but already the latest generation of SSDs is challenging the HDD for position in the data center and in all mobile devices." A prolific and versatile writer, Pam Baker's published credits include numerous articles in leading publications including, but not limited to: Institutional Investor magazine, CIO.com, NetworkWorld, ComputerWorld, IT World, Linux World, Internet News, E-Commerce Times, LinuxInsider, CIO Today Magazine, NPTech News (nonprofits), MedTech Journal, I Six Sigma magazine, Computer Sweden, NY Times, and Knight-Ridder/McClatchy newspapers. She has also authored several analytical studies on technology and eight books. Baker also wrote and produced an award-winning documentary on paper-making. She is a member of the National Press Club (NPC), Society of Professional Journalists (SPJ), and the Internet Press Guild (IPG).