Spin free: Balancing performance against cost with SSDs

While solid state drives offer increased performance, the key to figuring out the role they can play in the data centre is balancing that performance against cost.


While solid state drives offer increased performance, the key to figuring out the role they can play in the data centre is balancing that performance against cost.

SSD technology has been around for decades and has become more popular in laptops and desktops, especially among power users clamouring for the biggest performance bang for the buck. The word has spread and businesses are recognising the advantages of using SSD in the data centre to turbo-charge mission-critical applications. Companies can typically use fewer SSDs compared to the number of traditional spinning disks they would have to deploy to achieve equivalent performance.

However, not all solid state technology is built the same. The speed of SSDs doesn't come cheap; the average price per gigabyte is approximately 10 times more than traditional disks. Before adopting SSDs, you need to understand what is driving your performance needs and which SSD configuration is most appropriate for your applications.

Here are four hardware and software considerations for SSDs:

1. The need for speed: Are SSDs the answer?

In its study, "Worldwide Solid State Drive 2007-2012 Forecast and Analysis: Entering the No-Spin Zone," IDC forecasts the market for SSDs will grow 70% between 2007 and 2012, but adoption of this new storage infrastructure will not happen overnight.

SSD provides the power to significantly increase IOPS for the most demanding applications. It also frees up overtaxed traditional drives in tiered storage environments to function at maximum ability. Tiered storage moves data between high-performance, low-capacity drives and slower, higher-capacity drives. However, integrating SSDs into an environment not optimised for the technology can be a lot like fitting a square peg into a round hole.

To balance speed and cost, you should start small without having to purchase a lot of SSDs up front. Make sure you can maximise storage utilisation of SSDs by combining the drives with key virtualisation applications. See if you can integrate the technology in your existing array or if you need to install another "brick" or array to use SSD. Without the right infrastructure, the drives can quickly become too costly, difficult to manage and inefficient compared with traditional spinning media. When you're evaluating SSDs check with your vendor candidates to determine how SSDs can be integrated into their existing system and how to maximise functionality.

2. Drive vs. cache: Two ways to configure SSD

Once you decide to implement SSDs you must consider the actual configuration. The primary (and much debated) choices for maximising efficiency are whether you implement the drives as cache or persistent storage.

Cache-based configurations can improve the performance of a server or controller by acting like additional DRAM memory. Many controllers are essentially closed systems and won't accept cache cards, so the only option is to add a dedicated SSD cache, but that approach tends to be costly. Controllers that accept cache cards do so at the expense of a valuable PCI express slot, which would otherwise be used to maximise the number of ports. However, the biggest drawback to implementing SSDs as cache is that it prevents users from tiering storage, which many in the industry believe is the most efficient path to SSD utilisation and performance.

Unlike cache configurations, persistent, drive-based implementations let users tier SSDs along with traditional spinning disk. In an automated tiered storage environment, SSDs can be reserved for applications requiring the best performance, which means fewer SSDs are needed. Less-essential data that needs to be accessed quickly can be stored on relatively lower-cost, higher-capacity Fibre Channel or SATA drives, as opposed to being archived off-site or on tape. Automatically moving data back and forth between the solid state drives and disk tiers based on policies, such as frequency of access, can significantly reduce the cost of storing and managing the data.

The decision to implement the drives as cache or persistent storage maps goes directly back to the fundamental question: what do you want to achieve? Cache provides a significant performance improvement for the whole storage infrastructure, and does not require additional software or training. However, caching precludes easy tiering. When SSD is integrated as the top tier in a persistent storage environment, users can purchase only the number of solid state drives required to house the active blocks for their applications. They don't need to purchase SSDs for entire volumes.

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