The Use Case and Business Case for SSD

PwC is bullish on mobile, projecting a 35% CAGR through 2015, driven in large part by solid state disk (SSD) technology.  The PwC researchers now see it extending beyond mobile to other types of computing.

Deloitte takes SSD enthusiasm even further: By the end of 2012, SSD will likely store data in 90% of mobile devices (smartphones, tablets, MP3 players), up from just 20% in 2006, the consulting firm predicts. More surprising, Deloitte expects up to 15% of laptops and netbooks to rely on SSDs, four times more than in 2010. Even in the data center, SSDs could rise to 10%.

The growing penetration of SSD into enterprise data centers presents a  challenge to enterprise data center trying to identify the best use cases figure out how it fits into their storage strategy. Even with the price-performance improvements, however, SSD remains significantly more expensive than hard disk drive (HDD) storage on a cost-per-gigabyte basis.  Any adoption of SSD will require building a compelling business case for SSD.

“The increasing use of flash in enterprise solutions, explosive growth of mobile client devices, and lower SSD pricing is creating a perfect storm for increased SSD shipments and revenue over our forecast,” according to IDC’s 2012 market report.  The researchers expect SSD shipments to increase at a compound annual growth rate (CAGR) of 51.5% from 2010 to 2015.

The initial enterprise use cases revolve around workloads that require extremely low latency and workloads that demand fast performance or high I/O throughput.  It also can be useful in data centers scrambling to reduce energy consumption or are cramped for rack space. A small amount of SSD can replace a large amount of HDD in a rack.

For example, Penn State turned to SSD to speed up nightly backup. Its solution: a flash array from Texas Memory Systems (acquired by IBM) instead of increasing the number of HDD spindles. It paid off in a 6x improvement in nightly backup performance with two 1U flash arrays replacing 200 15k disks and reducing power consumption by 90% in the process.

With SSD prices dropping below $1 per gigabyte that still leaves SSD considerably more expensive than HDD on a cost/gigabyte basis.  Cost/gigabyte, however, is not the only cost metric important to enterprise data centers.

SSD has at least two cost metrics it brings to the party that you can use to build the business case for SSD:  dramatically lower cost in terms of I/O performance. This is particularly apparent when you look the I/O cost per second (IOPS).  SSD also requires considerably less data center energy and space.

The way you boost IOPS performance with HDD is to aggregate hundreds, or more likely, thousands of the fastest spinning HDDs to boost IOPS performance. Even at the low HDD cost/gigabyte, the cost adds up.

Also, few data centers these days have cheap rack space to spare so more rack space will need to be found, adding to the data center real estate cost. Finally, all those spinning disks consume electricity, raising energy costs so add to the cost of HDD the cost of data center space and energy. On a cost/IOPS basis of a few thousand HDDs, which is what it would take to generate a comparable level of IOPS to a just a few SSDs, the HDD approach is no IOPS bargain. SSD storage, by the way, uses 90% or less energy than HDD. Figured on a cost/IOPS basis, SSD energy consumption is negligible. This is the foundation of your business case.

This is not to say that SSD has no drawbacks. SSD life expectancy can be a concern. In short, SSDs can wear out.

The SSD industry has come up with several solutions to the wear out problem. The most widely adopted is load-leveling. Through load-leveling, writes are distributed across the cells to minimize wear of any cell. Through load-leveling organizations can effectively stretch the useful life of SSD by years.

It is unlikely that enterprise data centers will completely replace HDD storage with SSD. In the meantime, polish your business case for SSD. You’ll want it sooner or later.


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