IBM Makes Economic Case for All-Flash Arrays

In its recently announced flash initiative, IBM came to what at first may seem to be a startling conclusion: that all enterprise-class Tier 1 (i.e., high performance) storage should be flash. Let's not start a "disk is dead" movement, however, as disk will continue to play a major role in storage, such as for Tier 2 capacity storage.

Observers have predicted the end of hard disk Tier 1 storage for some time, but few expected it to happen within the next few years. While SSDs in the form of non-volatile flash memory have dramatic and well-touted performance advantages, their cost per GB of storage has been far higher than the best-performing hard drives. Conventional wisdom suggested that a good economic case could be made for using flash-based products only for that portion of storage that truly required high performance (and that was considered to be only around 5% to 20% of Tier 1 storage).

In contrast, IBM contends the economics favor flash over hard disks. How can that be? Most previous analyses compared flash memory with hard disks. When storage administrators use hard disks for performance applications, they typically only load a fraction of the data that drives are designed to hold to get the necessary IOPS. Because flash has no mechanical constraints, it can deliver similar or better performance in spite of being fully loaded.

IBM has taken a different tack. Computing is not just about servers alone, but also about the networking and storage resources from a physical perspective and all the software, including applications, that have to be put together to create a "system." From IBM's system perspective, flash uses less physical space and fewer network connections, which will impact and improve overall performance. Let's examine some of the other considerations from the example that IBM presented.

• 17% fewer servers -- Fewer servers mean fewer cores and fewer network connections, and also lower power requirements.

• 74% lower environmental costs -- Flash takes up much less floor and rack space, as well as being much more environmentally (and cost) friendly in terms of power and cooling.

• 35% lower operational costs -- IBM calculated the savings in server/storage administration (people time).

• Higher storage utilization -- While flash still costs more, 50% better storage utilization, lower maintenance and simplified management helps to ameliorate the difference.

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Now, all these are important reasons, but the cost for flash was still about $2.1 million versus about $1.7 million for disk. While $400,000 or so dollars is nothing to sneeze at, it wasn't the compelling factor that tipped the scales dramatically:

• 38% lower software license costs -- Software is the cost tail that wags the hardware dog; lower cores and other changes drive lower costs for database and infrastructure software. This is dramatic. In the example, IBM showed costs fell from about $5M to $3.2M; these savings of $1.8M dwarf the $0.4M.

Overall the cost with all disk was $7.1M, while the cost with all flash was $4.9M. This $2.2M savings meant a savings of 30%. In IBM's view, the winner and new champion is all-flash.

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