HDD versus SSD: What’s better for you? Solid state drives (SSDs) are displacing hard disk drives (HDDs) in corporate data centers at an accelerating rate. But HDDs are not dead yet. Each technology still has use cases for which it is the most cost-effective choice, and most experts expect HDDs to maintain a foothold in the data center for years to come. So, savvy CIOs and IT managers will need to assess the advantages and disadvantages of each of these competing data storage solutions for their own workloads.

In this article we’re going to examine how enterprise SSDs and the highest performing HDDs compare on a number of important features.


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HDD versus SSD: Performance

More than any other factor, it’s the speed advantage of SSDs over HDDs that has pushed them to the forefront in the battle for data storage preeminence. A recent benchmark study compared “the fastest consumer-grade” HDD with “the fastest mainstream SSD on the market.” In the random 4k write test the HDD achieved a rate of just under 208 IOPS, while the SSD came in at almost 30,000 IOPS.

Of course an IOPS rating does not definitively characterize the performance of a drive (depending on specific workloads, other measures like latency or throughput may be more important), but it does indicate the scale of the speed advantage enjoyed by SDDs. In general, SSDs can achieve a performance level that is up to three orders of magnitude faster than HDDs.

 

HDD versus SSD: Capacity

Enterprise HDDs of 10TB capacity are now on the market. These helium-filled devices represent the leading edge of HDD technology. And manufacturers remain committed to extending the capabilities of spinning disks to their maximum potential. Current expectations are that HDD capacity will reach the 20-40TB range by 2020.

But SSD capacities are already beginning to surpass those of hard disks. Samsung is now shipping a 16TB SSD drive, while Seagate has announced one that packs a massive 60TB into a single device. As these new high capacity SSD products demonstrate, flash memory technology is reaching density levels that spinning platter drives can never achieve.

 

HDD versus SSD: Cost Per TB

On a cost per TB basis, SSDs have already reached rough parity with the 15K RPM drives that currently represent the apex of enterprise HDD performance. For example, Zadara™ Storage, in cooperation with Intel, is offering SSD-based cloud storage at prices equivalent to those for existing HDD products.

At this point storage arrays that incorporate commodity HDDs still have a price advantage over SSD arrays for workloads that are not performance-intensive. But SSD prices continue to fall at a rapid rate.

 

HDD versus SSD: Durability and Reliability

Both SSDs and HDDs have characteristic failure modes that cause them to eventually fail. Sooner or later the moving parts of HDDs will simply wear out. SSDs have no moving parts, but each write to a storage cell degrades that cell by a small amount. Eventually it will reach a point where it cannot be written to any more.

Still, complete failures of enterprise SSD arrays rarely occur. That’s because techniques such as overprovisioning (providing more memory than the rated amount) and wear-leveling (which spreads writes over a larger number of cells) are widely employed to limit the number of writes experienced by any particular cell.

Overall, experience has shown that high-end HDDs (4TB+) have a failure rate of about 3.5 percent during the expected life of the drive, compared to a SSD failure rate of about 0.3 percent.

At this point SSDs and HDDs seem to have roughly equivalent longevity. Testing by Backblaze indicates that the median lifespan of a hard drive is over six years, while SSD life expectancy is in the range of five to seven years.

 

Carbon Footprint

Because its moving parts use power and generate heat, each HDD directly consumes about five times as much electricity as does an equivalent SSD. In addition, since SSDs dissipate less heat than do hard drives, and since their increased storage density means that fewer of them are needed to store any given amount of data, data center space and cooling requirements are significantly reduced. That translates directly into a reduction in an organization’s environmental impact.

 

TCO

For most corporate workloads, the acquisition cost of flash storage is still significantly greater than for HDD storage. However, when operating costs are factored in, the TCO for SSDs may actually already be lower than for equivalent HDD arrays. Use of SSDs reduces data center costs for power, cooling, floor space, rack space, and maintenance. And as SSD purchase prices continue to fall, the TCO disparity can only grow greater over time.

 

SDD Is The Future

It’s clear that when HDDs and SSDs are compared feature for feature, the advantage lies heavily with SSDs. The only thing HDDs still have going for them is their continuing (but continually diminishing) price advantage. When it comes to bulk storage of data for which the highest levels of input/output performance are not required, HDDs, either alone or, more likely, as part of a HDD/SSD hybrid solution, may still be the most cost-effective option. Clearly, however, the future of storage in the corporate data center lies with solid state memory, and not with spinning platters.


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