Enterprise SSDs: The Impact of Long-Lasting Storage

Enterprise SSDs that last seven years or more offer a low-cost alternative to slower spinning-disk storage and tape archives.

Th issue of SSD drive life is coming to the fore – the economics of solid state storage is being turned on its head thanks to the introduction of longer-lasting enterprise SSDs.

That's the conclusion of Randy Kerns, senior strategist and analyst at storage analyst Evaluator Group. Kerns was talking at the Flash Forward solid state storage conference in London in June. He says that flash-based storage is becoming far more durable than was the case in the past, and as a result enterprise SSD vendors like SanDisk are beginning to offer guarantees of ten years or more for some of their products.

In short, the SSD lifetime is getting longer – and with time will grow far longer.

"Dramatic Effect" of Enterprise SSDs

"When the lifespans of enterprise SSDs change, the effect is dramatic," he said. "It affects not just the running costs but also migration, and it overlaps with all the other things built in to the total cost of ownership. So this is huge, and it overwhelms the price differential between spinning disk and flash."

It's an important point because enterprise SSD storage remains stubbornly more expensive than spinning-disk storage in terms of cost per gigabyte to purchase. But hard drive storage systems are only designed for a useful life of about three years, after which they have to be replaced and the data migrated to the new hardware. If enterprise SSD systems need to be replaced far less frequently, the effect is a significant reduction in total cost of ownership (TCO).

Enterprise SSDs Allow Consolidation

With enterprise SSDs there's also an increasing TCO advantage derived from the fact that you need fewer or smaller storage systems. That's because enterprise SSDs are becoming much denser in terms of data capacity than conventional hard drives. For example, in March Samsung unveiled its PM1633a enterprise SSD, which comes in a 2.5" form factor and uses 3D NAND to offer a capacity of 15.36TB. By 2020 Toshiba predicts capacities of 20-40TB for hard drives, while enterprise SSDs could reach capacities exceeding 256TB.

TCO reductions stem from space reduction, but also from vastly lower power and cooling requirements. To get an idea of the scale of the space and power advantages of SSDs, consider this: 1PB of data could be provided by twenty five conventional hard drives — or many more if techniques like short-stroking are employed to improve performance — or just four less-power-hungry SSDs.

Storage technology changes rapidly, so the idea of a storage system that could last for ten years may not seem to be a great idea: buying one could lock you out of any new technological advances for the best part of a decade.

A solution to this problem, Kerns suggested, could be to disaggregate the controller from the underlying flash storage. "You could change the controller every three years, but change the flash every ten years – so you would look at the technology of controllers and of flash separately," he said.

Online Archives with Enterprise SSDs

As the longevity of enterprise SSD devices increases – new long-life flash may last fifteen years or more, albeit with a limit number of data writes – Kerns believes it will change the economics of enterprise SSD storage even further. For example, without the need for data migration more frequently than every fifteen years, the TCO of solid state archive systems offering fast data retrieval and low energy consumption could easily beat the TCO of tape-based archive systems. These latter offer far slower data recovery, require a high degree of management to ensure that data remains readable, and need to be upgraded every few years. For example, tape systems based on the LTO standard normally need replacing at least every two generations – or about every six years – and tape migrations can be time consuming as well as costly.

Despite the strong economic arguments for moving to solid state storage environments based on enterprise SSDs, Kerns said that in reality that's not a realistic option for most organizations.

"Most companies have a range of storage technologies already in place, and they have differing lifespans and amortization rules. And the cost of supporting these systems goes up as the systems age," he pointed out. "So what we find are buying decisions based on the lifespan of current systems."

Even when companies do make a purchase of solid state storage, they generally don't do so across the board. Instead, they move their Tier 1 apps in to all-flash storage systems, while using hybrid or disk-based storage for their other applications.

"You hear a lot about all-flash data centers, but in reality that's not how it works, says Kerns. "People move slowly, in a far more measured way."

That means that companies are likely to continue operating mixed storage environments combining spinning hard drives and enterprise SSDs even if – or perhaps when – enterprise SSDs undercut spinning disks in raw price-per-gigabyte terms.

(Kerns pointed out that price per gigabyte is rarely a relevant metric, because it only measures is the cost of storage at rest. "It certainly doesn't tell you about what the storage can do for you, otherwise we might as well all buy tape," he said.)

Enterprise SSD Price Crossover

Deduplication, compression and space savings will continue to help close the gap between spinning disk and enterprise SSD storage costs, and a price crossover is likely to happen in the next twelve months, according to Alex McDonald, vice chair of Storage Network Industry Association (SNIA) Europe. He said these factors will continue to drive down enterprise SSD capacity prices after the crossover.

He predicted that both host-based flash (using PCIe bus-attached flash acting as DAS) and all-flash arrays with built-in deduplication and compression will see strong growth over the next few years, but controversially, he is more pessimistic for hybrid arrays with both spinning and solid state drives and flash cache in the controller. "We are not seeing growth in that area – sales look like they are flat at best or declining," he said.

Why is that? McDonald believes that a few years ago most enterprises figured that all-flash arrays filled with enterprise SSDs would be reserved for high-performance workloads because of their cost, with hybrid arrays continuing to be popular in the mainstream for mixed workloads and scalable capacities.

But things have turned out rather differently, he said. In practice the deployment of all-flash arrays has gone much faster than predicted because many enterprises have swung their investment to new, next-generation data center infrastructure, and all-flash arrays are a good fit for that. Another reason is that all-flash arrays provide cost reduction through consolidation for existing data centers (as discussed earlier.)

There's also a valuable management-related benefit to all-flash arrays filled with enterprise SSDs that's attractive to many organizations: they are significantly easier to deploy and use as you don't have to configure them to mitigate the I/O limitations of HDDs. In other words, high performance comes out of the box without the need to mess about with short-stroking, striping, and other I/O enhancing tricks.

Enterprise SSDs Will Lead to Software "Gaps"

Today most enterprise SSD use is transparent to applications: they assume that they are talking to spinning-disk storage, and smarts within the controller software deal with the intricacies of working with a solid state storage medium.

But McDonald pointed out that as enterprise SSD performance increases – either using flash or other non-volatile memory storage – then the overhead from software operations, which currently accounts for about 10 percent of total I/O read latency, will become increasingly significant. He foresees a time when storage hardware itself is no longer the bottleneck, at which point we will need a new way of programming to take advantage of the enterprise SSDs of the future. "We are not filling in the software gaps," he warns. "We need to find a better way to read data: we can't think of it as disk storage."

The problem is likely to become more acute when products based on high-performance nonvolatile storage media such as Intel and Micron's 3D XPoint become more widely available.

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