November 04, 2009, 11:05 AM — There are many articles out there offering tips for getting the best performance out of SSDs – this isn’t that kind of article. While solid state technology will give users a boost in performance, we’re here to talk about the key to balancing cost and performance.
Solid state technology has been around for decades, and has become more popular in laptops and desktops, especially among power users clamoring for the biggest performance bang for the buck. The word has spread and now businesses are recognizing the advantages of using SSD in the data center to turbo-charge their mission-critical applications. Companies can typically use fewer SSDs compared to the number of traditional spinning disks they’d 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; in fact the average price per gigabyte (GB) is approximately 10 times more expensive than traditional disks. Before adopting SSDs, users must understand what is driving their performance needs, and which SSD technology configuration is most appropriate for their applications. Here are four hardware and software considerations for SSD.
1. The need for speed: Are SSDs the answer?
IDC’s study, “Worldwide Solid State Drive 2007-2012 Forecast and Analysis: Entering the No-Spin Zone,” forecasts the market for SSD will grow 70 percent between 2007 and 2012, but adoption of a new storage infrastructure will not happen overnight. IT managers considering solid state technology have to ask themselves a big question as they contemplate upgrades: “What does my organization want to achieve?” The resounding answer is increased performance, and lower latency.
SSD technology 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 optimized 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 maximize storage utilization of SSDs by combining the drives with key virtualization applications. See if you can integrate the new 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 to 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 maximize functionality.
2. Drive vs. cache: Two ways to configure SSD
Once users decide to implement SSDs into their data center they must consider the actual configuration. The two primary (and much debated) choices for maximizing the efficiency of the drives are whether they should be implemented as cache or persistent storage.
Cache-based configurations can improve the performance of the server or controller by acting like additional DRAM memory. However, adding a cache card to an existing controller isn’t an option in most cases, since many controllers are essentially closed systems. This means an expensive hardware upgrade is required to acquire a dedicated SSD cache device. Using cache cards in controllers with an open architecture takes up a valuable PCI express slot, which would otherwise be used to maximize the number of ports for server connections. However, the biggest drawback to implementing SSDs as cache is that it prevents users from automatically tiering storage, which many in the industry believe is the most efficient path to SSD utilization and performance.
Unlike cache configurations, persistent, drive-based implementations allow users to tier SSDs along with traditional spinning disk. In an automated tiered storage environment, SSDs can be reserved for data requiring the best performance for any application, 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 offsite 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 directly back to the original question: what does your organization want to achieve? Cache provides a significant performance improvement over the whole storage infrastructure, and does not require additional software or training to utilize. 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.
3. SLC vs. MLC: It’s what’s inside the drive that counts
For customers interested in solid state drives, there are two basic technology choices: flash-based solid state drives and DRAM-based solid state drives. Since the inception of SSDs, flash has changed the landscape and outpaced DRAM as the chosen data center technology. Although DRAM has performance benefits, flash is significantly faster than disk-based arrays, more affordable than DRAM to implement and is the widely offered format of most storage array vendors.
The flash found in these solid state drives is further broken into two categories: Single Level Cell (SLC) and Multi Level Cell (MLC). SLC flash is found predominantly in enterprise-class drives and, as the name implies, each data bit is stored in one cell. This format is linked to better reliability, improved longevity and better read/write cycles. MLC drives, while less expensive to manufacture, have slower transfer speeds, higher power consumption and lower cell endurance than single-level cell memory, and are typically found in consumer memory cards. The bottom line is more data is stored in each cell – if a cell is lost, more data is lost along with it.
4. Software applications to maximize SSD efficiency
Increasing speed of operation and access to critical applications is the impetus for investing in solid state technology. So once the hardware configuration is selected, users must find the software applications that will maximize SSD efficiency. Two storage virtualization technologies noted for their ability to make this performance spike a reality are thin provisioning and automated tiered storage. On top of these, users should also employ storage resource management (SRM) software to automatically track and report how much capacity is being used across tiers, and by the SSDs themselves. The most useful SRM software should provide the granular detail about utilization users need to take the guesswork out of SSD capacity planning.
This leads to a question every user should ask – are there hidden costs? Many solutions require investment in entire “bricks” and enclosures, which significantly increases the investment. Others allow users to purchase SSDs in smaller increments as the data set grows.
Additionally, will users be forced to predetermine volumes and applications for SSD technology? Can you use thin provisioning with the SSDs, or are you wasting capacity just to allocate storage? While thin provisioning is a storage technology that’s gaining popularity, few vendors offer this technology for SSDs. Thin provisioning solid state drives allows users to only consume space on these expensive drives when data is written, leaving them free of wasted space and operating at peak performance.
Another consideration is the ability to automate storage tiering. Incorporating SSDs can improve performance, but without the benefits of dynamic data movement to lower storage tiers, unused data remains static on the high-performance drives. This quickly negates the anticipated benefits. Since industry research shows that 70-80 percent of all data is inactive at any given time, automated tiering helps keep business data online, yet removes the need for administrative intervention or data classification software, saving time and money.
By combining thin provisioning with automated tiered storage, users can maximize their storage utilization of SSD for all of their business-critical applications, not just for some.
Conclusion: Getting value from SSD
SSD efficacy is based on the ability to increase I/O and utilization, so while the cost per GB may be higher than HDDs, the cost per I/O is far less with flash storage. This reduction is exemplified when looking at usage examples – some SSD suppliers suggest that one SSD can deliver the performance of 30 Fibre Channel drives.
As solid state technology moves from the periphery to the forefront of the data center, users are weighing the needs of their organizations. But before installing, IT managers must take advantage of efficiencies from storage virtualization options that give the most flexibility in deployment and type of applications that can use SSD.
While every data center may not need to process tens of thousands of IOPS daily, IT managers implementing SSD technology are future-proofing their organizations’ environments and positioning themselves to handle growth seamlessly. Furthermore, the value of SSDs can be measured beyond the data center to the desktop where the benefits of performance and access are experienced first-hand by end users. Providing lower latency can improve the experience of running database queries and processing sales reports, meaning the value of SSD technology can be measured both operationally and in business terms.
Bob Fine is Director of Product Marketing, Compellent
www.compellent.com
