Are the advantages of solid-state storage worth the investment?

Brien Posey examines the advantages (less heat, less energy than hard drives) and disadvantages (less capacity at a higher cost) of investing in SSDs.

For the last few years, solid-state drives have been all the rage.

The drives don't have any moving parts, which allows them to use less energy and produce less heat than traditional hard disk drives (HDDs), while also delivering better overall performance.

However, solid-state drives tend to have a lower capacity than is available in standard hard drives, and the cost per gigabyte of storage is much higher with solid-state drives. Given the cost differential, administrators must consider whether the advantages of solid-state storage justify the costs.

Before administrators can make an objective decision about whether or not solid-state storage is worth the investment, they must compare the cost of solid-state storage against that of traditional storage. Although prices fluctuate, you can generally expect to pay about 600% per gigabyte more for enterprise-class solid-state storage than for traditional storage.

The cost per gigabyte is not the only cost to consider. SSDs have total capacities that are far lower than even the smallest SATA or SAS drive that is being sold today. As such, an organization that decides to use solid-state storage might have to purchase a greater number of storage cabinets than would be required for traditional storage just to accommodate the sheer number of drives required to meet the organization's storage needs.

If an organization's primary concern is maximizing storage capacity or getting the lowest price-per-gigabyte of storage, then using solid-state storage would not even be a consideration. However, it is important to keep in mind that nobody would purchase solid-state storage if it did not offer benefits that justify its high price tag.

The main benefit offered by solid-state drives is performance. However, read-and-write performance benchmark data do not always do a good job of representing a solid-state drive's true performance. This is because a solid-state drive's greatest performance advantage over traditional hard drives is tied to random access. A mechanical hard disk must move the read-and-write heads across the surface of the drive to access data. A solid-state drive has no read-or-write heads. Instead, it uses an index to locate data. The process works similarly to the way that a computer locates data in RAM. The end result is that data fragmentation has very little impact on read performance.

If you are considering investing in solid-state storage, it is worth noting that not all drives are created equal. Like mechanical hard drives, some makes and models of drives can deliver far better performance than others. Benchmarking data varies wildly from one make and model to the next.

The question of whether or not solid-state storage is worth the investment primarily comes down to use case. It simply does not make sense for most organizations to go "all in" on their SSD investment. Instead, SSDs are better suited to use with servers on which performance is a critical factor, such as on a high-demand database server.

Even if an organization's performance needs do not justify the cost of equipping certain servers with SSDs, there may be a way for the organization to realize the benefits of SSD storage without breaking the bank.

A number of solutions exist that mix the use of SSDs with HDDs. Such solutions use SSDs primarily as a data cache rather than as primary storage. The "hot blocks" are dynamically migrated to SSD, while less commonly accessed blocks remain on HDDs. This approach can allow an organization to realize a tremendous increase in performance, but without having to invest heavily in SSDs.

For right now, this type of storage tiering must be implemented at the hardware level, which means that the approach is only supported on compatible hardware. However, the soon-to-be-released Windows Server 2012 R2 will offer software-level support for this type of storage tiering and block allocation.

Conclusion

Solid-state storage is a good choice for use in storage arrays in which performance is critical. Given the cost-per-gigabyte of solid-state storage, it is currently unrealistic for most organizations to deploy solid-state storage across the board. However, SSDs may prove to be worth the investment when performance is the most important consideration. SSDs are also a good choice for tiered storage because the caching of frequently accessed blocks allows the organization to realize a significant performance gain without having to completely replace their existing storage.

About the author:
Brien M. Posey, MCSE, has received Microsoft's MVP award for Exchange Server, Windows Server and Internet Information Server. Brien has served as CIO for a nationwide chain of hospitals and has been responsible for the department of information management at Fort Knox. You can visit Brien's personal website at www.brienposey.com.

This was first published in August 2013

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